how good they will turn out (and last) depends mostly on the initial prep and quality of materials used .....Imho, unless you are extremely hard on your wheels (ie racing) I don't think the extra expense of powdercoating your cars rims would be really worth it.
I painted my Triumphs plastic wheel discs about 6 years ago in two stage base-clear and they have held up very well even with repeated pressure washes and tire cleaning products....I've even painted my Focus rims with a rattle can with good lasting results and with that car I drove it in a much harder environments than my TR ever gets subjected to!
If you don't intend on doing it yourself, most large towns have Rim Repair Specialist's that should easily be able to handle wheel restorations, in my area the tab would be about 125$ per wheel for a standard refurbishing.
Ron.
http://web.me.com/rg_spb/TR7_Spider/Home.html