Officially, you are not allowed to park at a resort and visit a park, unless you are a registered guest at the resort, so as to not inconvenience those guests. Unofficially, if you valet ($12 plus tips), Disney often turns a blind eye, as the valets can usually park your car in a way that doesn't inconvenience those guests. However, this isn't a guarantee---if the valets are particularly busy, they'll be a bit more particular.
Additionally, it takes a good chunk of extra time to get to any of the monorail resorts, because you essentially have to drive *around* the Seven Seas Lagoon (in traffic) to get to any of them and get back, and that eats up a good chunk of time you might save by not dealing with the trams. Finally, the wait between trains on the Resorts loop is typically longer (and there are more stops) than on the Express loop.
I don't think it's worth it unless you happen to be eating at one of those resorts as well. That's the only time I would bother. And, maybe not even then, depending on the circumstances.