I have fiberglass enclosers reglazed all the time. They look good when the job is completed. The tubs I have reglazed are in rental units, and usually the tenants will use an abrasive cleaner and the tub will look scratched and dull again in as little as 2 years. I suppose if it is for your own use and the encloser is structuraly sound reglazing could be an option. The key to long life is using a non abrasive cleaner, and absolutely don’t use a bath mat with the suction cups on the bottom. There are numerous companies that do this type of work depending on where you live.