My doubt is regarding the cost and availability of parkiings in aspen city, Highlands or Buttermilk. Is it easy to find a place to park the car at that places?
Do you know how mutch more or less the parking can cost me per hour or for a day?
4 or more in a car is free at Highlands, Buttermilk is always free.
Parking in Aspen can be a bit of a hassle. I don't even know what it cost, because I walk.
A car can be nice, it's just not necessary. It will open up some options for accommodations, ie. you could rent a house up on Wood Run or the Ridge. If you stay at a higher service condo complex like the Crestwood, you won't really need a car. They have full time drivers with vans that will take you anywhere in Snowmass or the airport. If you stayed at a VRBO unit, renting directly from an owner to save money, then a car might be nice!
You will be taking a shuttle to get places, car or no. This is part of Aspen/Snowmass.
There is NO, NONE, ZIP, ZILCHO parking for Ajax Mountain and Highlands- mandatory bus ride to ski there. There is very limited parking at Snowmass, and there is slightly more at Buttermilk, but that lot tends to fill because people park there to take the bus to the other areas.
Renting a car will be less, not more convenient.
You can't park on the streets of Aspen and go skiing. I believe there is something like a 2 hour limit to park on the streets without the residency permit or whatever they have. The only other option is getting valet service at one of the hotels. Good luck with that.
Meanwhile, the bus system is free and ridiculously convenient, not to mention that most hotels in the area have their own shuttle. Public transportation is just fine.
Edit: Ok, I'm wrong. there is paid parking at Highlands. It still doesn't make any sense to rent a car just because the buses are too plebian.
We had a rental car for a week in Snowmass with no problems. We used the shuttle for skiing only. Drove for meals and entertainment in Aspen and had no parking issues. Since we weren't flying into Aspen, cost was better than a shuttle for 3 people.