If you don't want to polish and wax, the two main choices are Poliglow and New Glass 2.
http://www.newglass2.com There are also people who have used a no-wax floor product from, I think, Home Depot. As for purpose designed commercial products, Poliglow and New Glass 2 are THE 2 products. As noted above, I believe both products are an acrylic finish similar to no-wax floor products with additional UV stabilizers. There are plenty of posts on the main forum detailing people's experience with products like this. People who like the Poliglow and New Glass really seem to like it. People who have had problems have really had problems.
As for wax on buffed and polished gelcoat, the article I previously linked from MaineSail (Compass Marine of Maine) has information regarding proven products. Maine recommends Collinite paste wax (I forget the number. I have it, it's a tub of paste, which goes on easier when the area is spritzed with a mist of water.) He cautions against easy shine products that gain the shine from silicone oils.
For non-skid areas, I have used the TWO most quoted products, Woody Wax and Aurora Sure-Step. Woody Wax sprays on easily, but requires a fresh water rinse, which I don't have at my slip. I found it wears away quickly. I found the whole Sure-Step system with the cleaner and oxidized gelcoat removal product, followed by the Sure-Step seems to work well, but it's a royal pain in the a$$ to try and get the Sure-Step off the deep diamond non-skid pattern on an O'day. I think both products would work much better on new gelcoat, and would help maintain them, but are possibly not as effective on 25 year old somewhat neglected gelcoat. Unfortunately, I've never had new gelcoat non-skid to maintain. Maybe someday if I strike it rich somehow...