If a thread gets too big, then I assume it's full of sig spammers, so I just ignore it.
While that isn't a general rules, in most cases that is what caused the huge amount of responses.
I also reported spammy posts before, I just don't know if they got a permanent ban.
It depends on how you report it and whether they're really a spammer. If you report it in the lines of "Spam post - This user should be looked into", then they will surely be 'investigated'.
The best solution is if you just ignore the user by clicking on the on ignore on the left side under his nickname so you will not see any of his posts anymore
How does ignoring the majority of the content help anything? This just tackles the problem on an individual level, which was always present as a 'solution'.