- It would likely push more replies to low-quality discussions (threads) which displays signature and the regular bumping would make them occupy the first pages of the boards.
That's a good point. If that becomes a problem perhaps bump-score sorting can be implemented like in Altcoin Announcements.
- It could lead to more threads started for the purpose of being used as signature boosters.
Possibly but there are many of such threads already so it could remain at roughly the same level and accommodate the same level of spam.
I'm not saying that the suggested option would add a lot of threads of great content and somehow push spammers off those boards. Probably not. At best it would create more favorable conditions for a few more threads of better content. It'd be up to the users to take advantage of it.