"My Content" is very resource intensive, and many websites have reported major slow downs even using the settings I am using right now, so bumping it up would be risky. That said, if you are searching for a specific post, just search for the term + your nick, which works just fine and goes all the way back (just tried it). If you are trying to accomplish something else, let me know and I'll take a closer look at it.
I just checked your account, you should have all privileges, so I'm not sure what's going on.
I do know you can't renew until the sub actually expired. When was the last time you tried? The subscription software is really buggy (working on replacing it), so I keep finding weird issues like these.