I never understood the problem with horse armor.
Why does it have to do something mechanically to have value? If you like having a horse with armor, isn't that potentially valuable to you? Especially if it's only $2.
In fact, it's potentially better when things like that have no gameplay impact. If they have an impact, there are basically three possibilities:
(1) The change is so minor that it doesn't matter and the item really doesn't gain any value from it. (too many examples to list)
(2) The change isn't so minor.
OUTCOMES:
(2a) The change is a game breaker. (some of the DLC ME2 weapons, the ones that eliminate the disadvantage associated with a weapon class)
(2b) The devs have to waste additional time adding in some way to adjust the game balance to account for the change. (I can't think of any case where I've really seen this done)
(3) The item does something qualitatively new.
OUTCOMES:
(3a) The feature is so different that the item feels awkwardly tacked on. (too numerous to count, but a few of the ME series heavy weapons DLC can verge on this, some DLC characters in ME2 as well, though YMMV)
(3b) The feature changes the gameplay so fundamentally that it doesn't feel tacked on, but instead seems like a feature that just should have been in the game in the first place rather than DLC. (relatively rare, get it occaisionally with DLC characters, again, as in ME2)