I do it in decks with two different muster effects for 3 creatures to reduce the chance of ending up with duplicates of muster creatures in the opening hand. Has worked reasonably well for me. Never go over 30 cards though.
You want to draw your golds and silvers as often as possible usually, so mostly it is a bad idea.
However if you are consistently running out of cards in your deck that could make you go to a bit more.
I wouldn't get hung up on the number of cards in your deck. I mean, sure, it helps to have the right amount, but you know what they say:
It's not the size of the deck that matters, it's what you do with it.
currently there is no point to do that but as much as making a bigger deck is considered a bad decision gwent might actually change that taking in attention what deck-thinning mechanics we already see here so far