More stuff means more powerful players. Unless you add items such as
Wish or
Scry granting ones, I don't think that anything in the dungeons themselves will
break if you add more items. I mean, I guess that the Fire Node might be a funky place if your players bring along a Decanter of Endless Water, but that would probably be more amusing than anything. So if your players want more magic items, and you are happy with them becoming more powerful, I would be tempted to just give them some.
The gold and whatnot from a Hoard will not be hugely useful to them in the adventure - it isn't really the kind of game where building a keep or whatever is going to feature - but equally it won't hurt anything. Richer characters or poorer characters, either way they'll have enough money to sleep in the best rooms in the inn and carry eight months of trail rations, so I wouldn't frown too hard over that aspect of it.
I would probably suggest that, instead of adding Hoards, you just roll up/select some nice items that your players will enjoy, preferably elemental themed ones, and then add them wherever. I might do the same actually, since my players keep getting destroyed by the bad guys, and they could probably do with a nudge up in power to compensate for tears over dead characters
