Depends on if your current deck surface is paint or gelcoat. If it is gelcoat, then the faded appearance is just surface oxidation. (Not actually oxidation, mostly, but that's what people call it.) The only thing that makes it tricky to restore degraded gelcoat is when it has a non-skid texture imprinted into the gelcoat itself. That's what I am guessing you have?
I had really good success with my last boat with something with PTEF in it, and a LOT of polishing very small patches at a time with just my fingertips and a soft cloth. Machines don't really help with that project or, if they do, I certainly haven't figure out how to make that work. I cannot recall the exact product, but I suspect there are multiple options that are at least as good. Might have been Star Brite, but I thought it was a 3M product. Sorry, not very helpful.
If you are actually talking about paint, that is a completely different story. I don't know if there is much you can do with a faded painted surface, other than prep and paint over it. But, take that with a grain of salt - I genuinely don't know.
As you probably know, painting over gel coat is a one-way trip. I think the best thing to do is maintain your gel coat as long as you can before committing to painting over it. Once you've done that, you are committed to the painted deck. I think this is better than it used to be - paints last longer and wear better - but still more work than gel coat ... I think.
I am actually weighing options with my current boat's deck and considering whether it is time to just paint. So, my research on current paint options is in its infancy. Any knowledge/experience I have, along those lines, is 20 years old and wasn't very complete then.
