I'm pretty sure resort fees are waived for platinum members and I remember reading there is no resort fee for stays booked prior to March 1. If they try to charge an early check in fee, politely decline, store your luggage with the bellman and grab a bite to eat or a welcoming cocktail. Yes, on being able to pay the balance with your total reward points. It's been years since I've tried Rio's seafood buffet and I wasn't impressed. Things do change over time.
Remember, you and your wife are in Vegas, a city that rarely closes. Do what you want, when you want. Try not to over plan and ENJOY!
Back in Feb, Palms had new sign up promotions for out of town players. One promotion was a rebate, where you got some now, the rest in 2 or 3 installments. The other offered free play you could use now based on how many points you earned. Have you looked at slotplaycoupons.com? For $25, new sign ups can purchase $50 in free play at the Palms. If you already have a card, you can purchase $40 in free play for $25.
Cosmopolitan might have some type of free play or rebate for new sign ups. The thing for me with rebates is, will I be able to come back to town to take advantage of them. Some require one to come back a couple of times to redeem the full rebate. You might want to check out the details on the casino's website before making a special trip.