You can and should try it just once at least! There will be lots of tourists walking and looking and you can't tell who is who by their dress either. You don't have to be "dressed up" to go shopping.
Once time, a woman who looked like a "bag lady" was in one of the shops we were in and in about 10 minutes, plopped down big money and walked out with her purchases. We all got the giggles thinking we always knew not to judge a book by it's cover but in this case, we had and we were all shocked! It doesn't matter what you wear, the salespeople are generally snotty to everyone, they are paid extra to do that-lol.
Realistically, unless you are well off, you WILL be shocked at the prices and it might end up just being a disappointment to your daughters unless you prepare them in advance that you will just be looking and not buying! Make sure they understand that these prices are near the top of the scale and they might see things like a plain cotton t-shirt go for $500! If they can handle that, then by all means go and shop, heck, let them try on some stuff as long as you all understand buying is out of the question and they shouldn't even ask. I don't think that will be too much fun to shop and not buy so maybe take them somewhere else after to get their "fix" like the Beverly Center about 5-10 minutes away.
If you are "well off", do some planning in advance and pick something ahead of time to buy and then surprise them! When we were young, just turned teenagers, we went to Tiffany's "just to look, not buy" and my Dad had preordered gold bangles for each of us 3 sisters, engraved with our names on them. What a wonderful surprise and all these years later, we all still have them and I wear mine almost daily with the fondest of memories! They were obviously not the most expensive things in the store but we couldn't have asked for anything better.
Think about maybe something you would buy anyway, maybe a watch for example and price them on the web before you go to see if it is feasible. You can always call specific stores ahead of time and price over the phone. Maybe you could get them each a scarf or something small to remember your trip by-but be careful that it isn't a 5K scarf-lol.
You might even get lucky and see some filming. Years ago, we saw Charlie's Angels being filmed and saw Farah Fawcett-lol-mind you I was just a small young thing way back then. It was a drag though because you couldn't drive all the way around and parking was too hard but still, it was cool.
Years later, we saw Cheryl Ladd filming in Honolulu-funny but I guess that was my destiny to only see Charlie's Angels-lol. Couldn't have been Tom Cruise or some other handsome man...