Hello, I had a Blast for about 4 years and didn't mod it, but here's what I recommend. That water cooling system is a very good investment. I don't think the stock prop is very good; I began to have pretty bad cavitation problems after a while and couldn't seem to clean up the prop enough to stop them. I think a metal prop of similar size and pitch could be a good investment. Also, even more important is replacing the stock U-joint. It makes a lot of noise and really grinds when you turn. If you do any mods that increas the speed, you might want to consider installing a turn fin -the Blast tends to spin out on sharp turns and on choppy water. I think your electronics/motor should be fine. Just mind the 17+ (I believe) turn rating of the Nautica ESC. If you drop in a hotter motor, you might have to upgrade the ESC too.
Hope that helps!