I would say if there is going to be any limit, it would be new players ability to post threads in General discussion. It may seem unfair, but I think that is where most of the repeat threads come from since they are much less likely to make any attempt to use the search function. There are less competent veteran players, but they just can't get right.

There is also already the new player help forum where there should be no limit on their thread creation. I think after a certain character level, they should no longer be considered a new player and be allowed to post in general discussion. These limits should not be extended to any of the other forums like bug reports or feedback forums tho, because those things can be given from lvl 1 on and it is highly unlikely that those forums would be abused with repeat threads and useless spam.