Nahh, Hollywood does Vegas a disservice. It's mostly full of American tourists who, bless them, are not known for their glamour.
I only spent a few days in LA, and mostly in Santa Monica at that. I would say, at a push, that it really doesn't matter what you wear. Even in the nicest restaurants, most of the clientele are dressed casually (expensively, maybe, sometimes). I'd go for neat, classy casual stuff: good jeans, nice shoes, that sort of thing.
In my experience bars and clubs in the US are a lot more relaxed. I've never come across anyone who was as anal about trainers, for example, as English club bouncers.
I have also cruised a lot, and always get a bit annoyed that it's the Americans that let the side down. They are either glammed up, white tie and thousand dollar dresses, or slobbing about in shorts and polo shirts.
You'll be fine. They want your money, honey, they're not so fussed about what you're wearing 
Have a lovely time. Go to Mulholland Drive whilst you're in LA, the views are amazing, and Venice Beach. The rest is a big car park.