The Value Resorts have something called Luggage Assistance, which, from what I understand, is a service that you have to make an appointment or reservation for, at least in terms of pick-up and delivery.
The Moderate Resorts have Bell Services, which is basically an on-demand luggage pick-up and delivery service. However, there may be times when they're absolutely swamped and won't be able to give you immediate service. And at the moderates, "immediate" is a relative term because the resorts are so spread out, that it takes time for the CMs to get from between locations (unlike a high-rise hotel where it's just a matter of riding elevators between floors).
As for luggage storage before and after check-in/check-out, every halfway decent hotel in the USA offers this service, and WDW resorts are no exception.