I'd definitely delete a lot of them. There's so many posts that I just don't want to ever run into with super cringy things from when I was younger or just cluttered threads I don't have a use for (like some of my map/mesh/etc. related threads).
I probably wouldn't delete a lot of posts. Sure, basically every single one of my posts to this day is just.. awful to look at, but I'd only want to get rid of the particularly cringe worthy ones (I can even think of a certain few right now I'd smash to bits with a hammer if I could). Besides, I have so many stupid posts it would take a long time to go through them all xD
Interesting question, though!