A lot of vB5 forums do get styled, at least to some degree, and in my travels round people's sites doing support I've seen some extremely nice ones....from fully fledged new themes where someone has clearly rewritten a lot of the style, to simple colour changes that really work and give the site some identity.
One of the things I personally feel does vB5 no favours at all, is that its default style is rather drab. Even if it were a brighter blue, it'd be nicer. Some of the 'themes' that now ship with the product are very nice and they provide a decent starting point to style the rest of the site.
Just to give an example:
This is my cloud demo site:
https://www.adminammo.com/
I used the 'Black Red' theme as the basis for the style, but the css is heavily customised to move the look more towards the 'traditional' forum layout...a bit like vB3 and older forum scripts like XMB. Everything back in boxes, etc.
I'm not claming it as a work of genius, but it shows what can be done with vB5.
AND - that is a cloud site. So no templates were changed, as cloud sites don't allow it. It's all done with additional css.
I've done styling work for dozens of vB5 sites who upgraded from vB4 and wanted their 'old' look and feel back. Mostly I stick to stylvars, colour changes and custom css, because changing templates just causes problems when they next upgrade.