Pimped up titles usually deter me from reading a story, because I dread the amount of cheesiness I might find in it. I tend to avoid them for days or weeks, until I'm just too bored for anything else. But once I give it a chance, my decision to come back is only based on the content, not on the amount of pwetty dots or hearts I find at first glance.
Therefore, I don't think you should outright forbid authors from adorning their thread titles. Encouraging the glitter aficionados to refrain from over accessorizing would be a better course of action. That way, you don't come across as a tyrant, and newcomers don't get scared with (y)our pettiness. xD
Also, I'm inclined to believe that people here have enough common sense to make things work without having mods or admins breathing down their necks, so it shouldn't be much of a problem. But if it gets really bad and there are complaints about it, you can pull a Miki and glare/grope/molest/whiplash the offenders into submission, or you can set some rules about the title format after the forum is reorganized. Not just because it pleases you or any other member here, but because it would keep things easy and simple in the long run. (Yet I hope we never reach the point where rules are actually needed...)