Filling up repeated answers to the thread where even the creator of the thread do not turn back on it. Cleaning of old threads with too many pages of repeated replies would help kick out spam posts. Just read through the replies. Sir Yahoo's reply can be brought to the screen. Auto deletion of old thread with too many pages would reduce the work of moderators and managers. This would wash out spam threads as well.
I think if that happens that having implement auto deletion thread will lessen spam post, 15 to 20 pages that are already good enough getting a perfect answer in every thread that asking or sharing an idea in each thread. Mostly they NOT mind to the middle replies to the OP's thread, mostly they are reading the page and the last page of the thread.
Auto lock or auto deleting a thread if reach the maximum pages which is a good idea in MEGAthread only.
To add some suggestion, it is better to include how many merited replies are there in the topic so that people could only read the useful comments that would help the forum. If we can add a "Merited Replies" button which are already filtered (just like we view our own sent & received merits), the readers could easily find their answers to the question of the OP. This would really saves time on the reading part of the member. Gaining Knowledge in the forum would be faster which could also result to a healthy discussion in the forum.