Were the spoils of piracy really worth the effort during the Early Modern Period? How much money could the average pirate really expect to make from leaving the Merchant marine and joining a band of Buccaneers?
Was Privateering really an effective strategy for National policy? Or was it only good for picking fights with other nations?
Not sure that there is a specific answer to "how much money could the average pirate really expect to make." What a pirate gets is all dependent on many variables that could result in pirates receiving several thousands British pounds sterling worth of valuables per share or basically nothing. But since some people were able to successfully be pirates, others saw it as worth a try when the right circumstances presented themselves (though some may have not thought through what the "end game" would be after successfully pulling it off and wanting to not pirate anymore, if they survived it and didn't get caught).
Was privateering effective for waging war? They kept on engaging in privateering for a notable period of time in terms of maritime history. In terms of decisively shifting a war, I'm not sure if privateers can claim that title (we'll see if anyone ever writes an article or book on that and argues for it), but they had an impact. The privateers that has the specific mission of seeking out and taking/destroying commerce (the 'commissioned private men of war' so to speak, and not the merchant vessels that get letters of marque so they have permission to "hey, if you see an enemy vessel as you proceed along with your other main commerce ventures and think you can take them, go ahead and do so") had their impact of damaging a country's economy. Plus the government often gets a cut of what are deemed legal captures and there are the economic benefits of selling the ship and cargo of said captures back home. There is also the trade off of hurting your enemies without expending money to build, arm, equip, and man a ship out of the government's pocket. Ships cost a lot of money just to upkeep them, let alone build. If the private sector is willing to help out, why not take the opportunity? Money from the government can go into maintaining the Navy fleet for decisive fleet actions and control of the seas. The private sector will build the vessels that are good for raiding commerce, especially since said vessels are easy enough to convert afterwards for commercial purposes. The Navy can concentrate on building warships that can stand in line against the enemy fleet.