Roughshod, in the area I'm from (US west coast), in my experience and from what I have read, refers to the use of caulks or caulkins on horseshoes to improve traction and increase the wear life of the shoe. Traditionally, caulks were projections from the toe (one caulk) and the heel (two caulks) forge welded or forged while making/shaping the shoe. More recently, a variety of screw-in devices have been developed to improve shoe traction. These, too, are called caulks. The downside to using caulks (pronounced corks where I'm from) is that it tears the hell out of trails and is extremely dangerous on hard surfaces because you reduce the surface area of contact so dramatically. I would assume that cobblestone streets, like trails would suffer from sustained use by roughshod horses.

You do not want to be stepped on by a horse with caulked shoes. If, as you say, the origin of rough-shod has to do with the damage a shoe makes to the enemy in battle, then caulks would definitely make a difference. After all you are reducing the bearing weight surface of a thousand pound animal to a few square inches. Edit: more words

The concept of roughshod (i.e. where the shoe nails are left proud for better grip in poor conditions - mud and snow) is extant from at least 1688 (OED listing). Robert Burns uses the phrase in it's current connotation in his epistle "Election Ballad" (1790)

Now, for my friends' and brethren's sakes,
And for my dear-lov'd Land o' Cakes,
I pray with holy fire:
Lord, send a rough-shod troop o' Hell
O'er a' wad Scotland buy or sell,
To grind them in the mire!