Tl;dr: the right to a jury trial is not as broad as it appears at first glance, but the founders probably intended it to be quite broad and comprehensive whenever it actually does apply.

I’m a constitutional lawyer (though not a professor) and can give some info here. There is very little extant evidence of the drafters’ intent with respect to the $20 aspect of the 7th Amendment, because it was added in a closed-door session of Congress. The drafters and other founders were absolutely aware of the possibility of inflation (though it did not at the time have the same steady march upward that we have become used to in the modern era). Some scholars, such as Columbia law professor Philip Hamburger, have argued that the $20 clause was actually intended to become less valuable due to inflation, that the founders wanted to use inflation as a way to phase in a stricter jury requirement over time. I’m not entirely convinced by his argument or his article on this, but then again I’m not a lauded Columbia constitutional law scholar. So it may have been an intentional way to increase jury usage over time, but that requires a good bit of assuming and reading between the lines.

One thing to keep in mind: it is rare that a case worth less than $20, now or in the 1790s when $20 was the equivalent of about $300 today, would be brought in federal court.

There are two types of federal jurisdiction: diversity jurisdiction, and federal question jurisdiction. I won’t get into too much detail, but diversity jurisdiction applies where (a) the parties are residents of different states, AND (b) the amount in controversy is above $75,000. So diversity cases will never have to consider the $20 minimum because they would not be allowed in federal court.

As for federal question jurisdiction, these are any suits of any amount related to issues arising under federal law (as opposed to state law). These suits could involve amounts less than $20 (or $300 if it’s the 1790s), but will they? Occasionally someone might bring these cases for principle or for advocacy reasons, but generally people bring cases because they want money. And rarely is anyone seeking financial compensation going to put in the time, effort and expense to bring a case for $20/$300.

So, thinking about it this way, the point the drafters may have been making here is just that while claims without any actual allegations of financial damage will not be permitted to have a jury, in general cases at common law in federal court will have a guaranteed jury right. In this sense, the $20 requirement may have been meant to be largely symbolic.

I have not gotten into a couple of issues here that come to mind. Cases covered by the jury trial requirement are only cases “at common law,” which is a more technical and historical term than it appears and excludes a wide range of case types, such as those at “equity”—e.g., admiralty cases, cases against states, and certain “equitable remedies” such as estoppel, meaning generally orders stopping people from doing certain things but not requiring them to pay money. Also, parties can and often do waive their right to a jury.

Economist rather than historian but history of economics is a total nerd out topic for me :)

The skinny answer is that there was no such thing as monetary policy when the 7th Amendment was written, inflation over the following 120ish years was negative and it was 140ish years later that the importance of low positive inflation became policy.

Longer answer

Economics is young

The colloquial answer to where the field of economics originated is usually Adam Smith but in reality while Smith taught us to think about economics the field was indistinct until around 1920 when economists like Frank Knight originated economic empiricism. Prior to this economics was part of political economy and economic theories were almost always bound up in politics, heterodox schools like Marxist and Austrian which originated prior to the birth of empiricism still exist today and have a similar attempt at defining economics in political/sociological terms but are extremely fringe and don't contribute to mainstream study.

In general economics before 1920 was nonsense (obviously much after too but ~1920 can be considered a general cut off before which economics basically didn't exist) and full of people presenting stuff they thought up as theory without the slightest evidence to support their conclusions. Its totally ok even today to have ideas like this but you have to actually be able to prove them now.

This drive towards empiricism originated econometrics (the statistical study of economics) and the general use of math in economics. Modern economics is extremely math heavy with most economists having an advanced degree level of mathematical education. We study complex systems using math.

This is also when we first started to consider micro and macro economics as distinct things with distinct theory and policy implications. Today we generally consider economics prior to ~1920 to be micro focused almost entirely, focused on the actors not the system, which largely accounts for the errors in thought.

Economics basically didn't exist until the 1920's.

Where modern monetary policy came from

For a much longer (and better) discussion of this topic I suggest reading Friedman's A Monetary History of the United States which remains an important text even today.

The 1800's and early 1900's are noted as a sequence of massive banking crises, failures and general economic insanity. Countries that were not the US generally used their countries central banks to help absorb some of this crazy but as the US lacked a central bank we were fully exposed to these enormous swings.

Eventually the US formed a central bank in 1913 in response to the banking crises and things began to improve. The political and legal framework under which the fed was created, that its decentralized and without direct political control, was not intentional (rather the only way it could be formed in the US) but turned out to be correct and a model that has since been replicated around the world.

Unfortunately the field of economics was too young to develop a good monetary theory and so fed policy in the late 1920's ended up turning what should have been a short & sharp recession in to the depression. Monetary policy continued to make it worse until 1932 until a policy change allowed recovery to start. The Fed & Treasury did it again in 1937 though but thankfully not as bad.

The origin of modern monetary policy was around this time with Keynes work, discussed in his general theory published in 1936, which created a general framework for business cycles and how monetary policy influences them. In the post-war years this led to central banks seeking to keep inflation & growth generally stable.

Monetary policy post-war to the early 1980's was a massive improvement over what came previously but there are still many examples of bad policy causing recessions or other problems. The inflation problems of the 1970's were compounded by the the slavish devotion of the fed to the Phillips Curve which is a model explaining the Keynesian relationship between inflation & unemployment.

When the Phillips curve madness collapsed in the early 80's the work of Milton Friedman & friends, who had largely predicted that the Phillips curve was about to break, heavily influenced replacement policy. This regime is largely what we operate under today. Inflation targets were introduced in the early 90's (but are becoming less important today) and we started using QE in the mid 00's.

The observation that the neoclassical theories of monetary policy were more correct than the classic Keynesian models led to some more work during the 80's which resulted in the neoclassical synthesis. This merged Keynesian & Neoclassical schools in to the single mainstream school we have today (aka the Keynesians agree the Neoclassicists were right and the Neoclassicists agree to be called Keynesian) which has greatly helped advancing theory since the 80's.

Monetary policy didn't really exist until the 1930's (but with early attempts from about 1890) and it took until the 80's for us to get it right on purpose.

Prices

The absence of central banks seeking stable rates of inflation and regulatory & central banks managing banks means prices up until the early 1900's were all over the place. Pricing estimates show some years with double digit inflation and some years with double digit deflation. Average inflation during the 19th century was actually negative as a result of this.

While today we know this is bad we didn't have a good theory of prices until the 1920's and didn't understand the importance of inflation until the 1930's. We still don't understand how to manage inflation super well (particularly deflation which is crazy dangerous) but had nutjob theories about it until the 1980's.

Quick note about growth

Good inflation is a natural consequence of growth, it needs management to avoid getting out of control but a healthy growing economy should experience inflation.

If you look at economic growth estimates in history its more or less flat before 1800 (growth that did occur was largely due to urbanization & population growth with a few bumps due to classical empires like the Romans). Industrialization then started in the late 1700's resulting in a continuous increase in growth rates since.

Bill of rights was too early for inflation

Those writing the bill of rights were a little early to know about inflation, economics or growth.