MostlyHarmless42
Adventurer
What? No! If a thief can make boots immune to them for his friends then everyone else would have them too.
Pretty much this, obvious caveats being the assumption that it is a common enough practice and something people could afford or access. Would I allow a player to make it? Sure, but enemies would have them as well if it is realistic to do so. And a merry arms race between making better caltrops and anticaltrop boots would ensue.
Also I'd probably consider making them some sort of attachment or special boot, and give them advantages / disadvantages. For example, snow shoes are great at walking on snow but awkward as all heck when trying to use them otherwise and no sane person would wear them except for when they are needed. And I'd imagine such an attachment would cause issues with other things like the above post mentioned the tearing of carpets or scratching if floors.