This could be implemented and users filling out google forms for bounties has been suggested before but we still need the merit system. Bounty spam is currently confined to their own threads and boards whereas signature spam is spread out all over the forum and this is why we need the merit system (or something like it) to help curb that or more importantly reward quality contributions. More measures still need to be put in place to curb spam of all kinds though (bounty, bots, sig spam etc) but bounty spam is far from the only cause of spam and is probably the least of the issues right now, but nice try  .