I'm a noob so I was wondering.
I've gone rooted and non-rooted, and I'll stick with non-rooted. I never saw a big leap in battery life unless I disabled the functionality of the phone. I see no reason whatsoever to delete Sense UI and download Beautiful Widgets which look pretty amateurish (admit it) compared to Sense. It's no fun to root and leave stock, and half of the ROM's out there kill or disable one thing or another that worked fine under the factory ROM. If you like messing with the phone, go for it. If your phone is absolutely CRITICAL to you, don't.
I find some of the Beautiful Widgets to be very well done. Sure some look like crap but I would say some of combinations look a great deal better and have far more character than the stock Sense Widgets. However that has nothing at all to do with rooting. Beautiful Widgets are just another set of Widgets that can be used rooted or not. The BAMF ROM Im running now doesn't even delete Sense anyway, so again I dont quite see your point there.
That being said I can see people not wanting to root for fear of disabling their phone in some way. For me however the speed of the OC and the battery savings of on demand CPU throttling alone make it worth it. Also getting rid of the Apps Verizon force feeds you is a nice byproduct of the whole thing. Some dont affect anything at all of course but I like to have control of what apps exist on my phone.