Well done on getting those G's!
I agree that this year we did find Vegas more pricey than before, the main issue being the exchange rate (oh I remember those happy days of $ 2 to the £
) But we also found that a lot of the hotels are "enhancing" their dining options to "celebrity chefs" - GR is everywhere!
You mentioned using the buffets for breakfast/dinner - ISTBC but there are no discounts for children and so you could easily end up paying $$ - for example the Wynn buffet is around $ 20 for breakfast increasing to $ 39 for dinner (excluding weekends)
per person before the 8.15% tax and tip. I believe that the Caesar's Group offers a "Buffet of Buffets" 24 hour pass which covers their properties although an additional fee will be charged if you want to eat at Caesar's itself.
https://www.caesars.com/las-vegas/buffet-of-buffetsAs Clanger says we always stock up on snacks that don't need a fridge and water from a CVS or Walgreens - there are loads on the Strip, and I think the nearest one to Wynn is either at Treasure Island or Palazzo/Venetian. There are also plenty of fast food chain places around, such as Subway, McDs, White Castle, In'n'Out Burger etc.
Being at the Wynn you'll be right opposite the Fashion Show Mall so I'm sure your daughters will be happy with that for something to do
There are some sit down chain restaurants there but on the top floor there is also a food court which is very reasonably priced - we always eat from Panda Express there for around $12 for lunch for two at least once every trip.
We had a really nice meal at BLT Steak at Bally's in May using a Travelzoo voucher - we paid $ 115 before we went but had $ 210 of food & drink (before tax and tip). This was a deal for two but they also do a deal for four which is $ 225 for $ 420 spend before tax & tips. Their menu is on line so you could look before you get the voucher to see if it would be worth your while.
We used a MyVegas reward for Tender at Luxor which was $ 75 off a $ 150 spend, but as you're going next week and staying at the Wynn then MyVegas will probably not work for you though.
As well as the Fashion Show Mall there are the North and South Premium Outlets. We prefer the North but beware - it is all open and there is no cover so you will melt in July! The South is covered. I'd suggest registering for their VIP scheme before you go and printing off the reward voucher, which you can swap at the Outlet information centre for a discount booklet (they did accept screen grabs this year on my phone).
There's more shopping at the Forum Shops at Caesar's Palace, which has the Atlantis show during the day, and the Miracle Mile down by Planet Hollywood. The advantage of these shops is that they are all air conditioned!
We really enjoyed going to the Neon Museum but that is out in the open, if you can get tickets so close to going. They also do a joint ticket with the Mob Museum, and there are often Groupon and Travelzoo discounts for these. The joint ticket is very highly rated.
There are the "free" shows of the Bellagio Fountains, Mirage volcano, the small fountain outside the Wynn (by the bridges to Fashion Show Mall and Palazzo), the Lake of Dreams at Wynn at night, and just the sheer over the top-ness of the strip. At the bottom of the strip by MGM there is M&M World and Coca-Cola Store with flavours from around the world!
I'd strongly recommend that you wear
very comfortable shoes, drink lots of water and use plenty of sunscreen!
One thing that you will come across on the strip though are the "characters" and "show girls" who will hustle for you and your daughters to have photo's taken with them and then expect a tip. There are also the water and CD sellers - so as Burt Bacharach says "Walk On By" ..... (the CD sellers will also be at Venice Beach if you go there when in LA and we found them more "assertive" at Venice Beach than in Vegas )
A car is great for getting away from the Strip - we went to Red Rock Canyon, the Hoover Dam and the Shelby Factory (although the Shelby Factory is only just past the "Welcome" sign) and to the Outlet Mall this year. But if we stayed on the Strip we used Uber and Lyft all the time - our most expensive Uber was $ 9.06 from Aria to the Car Rental Centre and Lyft was $ 8.53 for the 10 minutes it took to crawl from Aria to Mirage at 6.30 pm at night!
The downside with having a car in Vegas is (if you do not have some status with the various Players Clubs) then you will have to pay a daily fee for parking, which varies between hotels and whether self park or valet. At the moment Wynn only charges for valet, but they are installing the gates and pay machines for charging for self parking so it won't be long ...
We had six nights in Vegas this year and as Pearl we could self park at any MGM resort for free.
In terms of bars then I'm pretty sure the girls won't be allowed in for soft drinks unless there is also a restaurant. Certainly in the bars we frequent (Parasol Down at Wynn, Lyft at Aria, Baccarat at Bellagio) there were no children. You'll also find the majority of bars do not bar smokers.
Have a fantastic time in LA and Vegas!