|Think about Loose Coupling|
As far as how the site looks: There's plenty of flexibility available to you if you want to tune up your stylesheets. I wouldn't want any serious changes in looks, though. I'm pretty happy with it as-is.
Speeding things up would certainly be nice, though. I don't have enough time left in the day to learn the inner mechanics of the site to try to speed things up, though, so I won't complain about it. I've seen several suggestions for speeding things up a bit (such as turning off the nodelets on preview) so I expect that some tune-ups here and there will probably percolate through as time permits.
Since I've seen several requests like this, I'm just curious: Just what is it you want to see? If you leave the structure alone so that the site basically works as-is, then I'd expect you to propose:
Without concrete suggestions for actual improvement, it just sounds like change for changes' sake. (In other words, a lot of work for no benefits.)
UPDATE: One minor note: One reason I don't care for more "modern" designs is they tend to stuff plenty of whitespace on the screen to make things pretty. I have a couple large monitors on my home machines, and I still wish they were larger. If I'm digging for information, I just want as much as I can get on the screen. The bells and whistles are nice for things like watching videos and such, but I'm not here for that. As hominid mentioned, I'm here for the content.
That doesn't mean that I think PM is a pretty site, it's just that I think making it more attractive will make me scroll more, and that's a big turnoff. Having said that, if you post a style sheet to make stuff purty, I'll give it a try and offer suggestions on it, if you like.
Update: Struck out the bandwidth complaint: Now that I'm monkeying about with a style sheet on my box, I've started looking at the text of the pages PM is sending me, and there's a huge amount of stuff to support style sheets. Thus, I don't think a few K here and there will impact the bandwidth as much as I initially expected.