I had a Clackacraft that I bought off a buddy, he Arma-coated it and we both really liked it, it was a slick, smooth finish that didn't change the rowing characteristics much if at all, it also took a little of the flex out of the fiberglass. He had the boat for a year or so before he coated it and it had a # of cosmetic scratches and dings, after coating we had the boat for 5-6 more years and it never showed any scratches/dings.
As for cost, he worked at the Kent Arma-coating before they closed up shop, he did it one night after work for nothing, It seems like he said it would have cost 3-400 bucks. As of 2 years ago, there was an Arma-Coating in Sequim across the street from Costco.
When I get my next DB, it will be glass and I'm going to look for an A-C shop.