But if you get some soot, or airplane smootz, or a lot bird DROPPINGS...then I'd wonder about that too.

If you're always cleaning the boat (like every day or so) when you're in harbor, then it doesn't build-up.

If you really clean the boat well only one or twice a month, then I'd also factor that in.

I thought the Interlux system look pretty good -- but I have no first hand experience.

If believe that if you're going to be painting over cosmetic "spider" cracks, you really need to fill and fair them; or else, they'll just come back or telegraph through.