I usually give the signed cards away...or simply don't ask for them back. So I too fall in the "Piles of excess cards" category. There is a ton of stuff you can do with these cards. You can organize them into new decks every so often. You can also use them to make card gaffs. That is what I mostly do with the extras. You can also practice those destructive techniques with these. TnR effects, Mercury card folds, and other stuff like that.
My experience with giving cards away as a "souvenir" that people don't keep those cards. Unless its like anniversary waltz or something like that or kids keep signed cards.
So if the spectator doesnt keep the card, theres no reason (in my opinion) to give them the card, and to the magician that signed card has more value by keeping it in the deck.
Interesting...and true point. That said, when I say "Don't ask for it back" I simply mean that the trick is over. Generally the card is in their hands. If they go out of there way to give me the card back then I just take it but it usually goes in the "practice Mercury card fold" pile, not back in the deck. I just hate it when other spectators pick an already signed card. Don't know why....Akirafist actually has a pretty good line for that occasion! I guess it is just that at my heart I am a card guy and thus I am picky about cards. I even have enough of a collection now that I can coordinate the right cards with the right outfits and occasions!
You know, Fourniers for high born snobs wearing tweeds at a country gathering.
Anglo Rugs when a Tuxedo is required.
Bicycle Rider backs when I am performing for low class hillbillies with no taste wearing wife beaters with mustard stains.