Even just from a simple comparison:
Bitcoin Discussion (which is bad enough): 232.6K Posts, 93.7K Topics
Altcoin Discussion (which is far worse): 320.9K Posts, 100.1K Topics
There has been positive changes with the Altcoin sections though, the implementation of the bumping system helped with reducing the amount of fake bumping or at the very least prevented most users from ever seeing it. So, despite it still being of lower quality compared to other sections in the forum, there has been improvements in the last few years.
Now, how we actually combat it further without stating the obvious; removing the possibility to run bounty campaigns, I really don't know. As far as I can see as long as these are allowed, and altcoins remain popular there will always be a spam problem over there.
Bitcoin Discussion still has its lower quality posts, and this isn't because of bounties, at least not primarily. So, its obviously an issue outside of bounties also, which means removing bounties probably wouldn't eradicate the issue inside the altcoin sections either.