Maui isn't the place to go if you're pinching pennies. Worrying about a car parking fee, etc.
I'd rent the car and not worry about it, just enjoy the flexibility it'll give you. It's a LONG uber from Ritz to Wailea.
If you have to pay to get out and see anything in an uber it's going to add up anyway. There's nothing up by the Ritz and in 4 days you're going to want to have left a few times to explore that part of Maui
11 days on Maui and no trip to Hana? You need a car for that for SURE.
Can't speak to your upgrade chances. Enjoy Maui..