The switch "might" respond to a shot of switch cleaner followed by water repellent lube. If not, it's probably a bog-standard mini slide switch, readily available. A friend has a Dragon (very similar, a bit longer) that he went to town on waterproofing. He used a magnetic switching device so that switching on and off did not require any internal access. BTW we sail in salty water, any corrosion possibilities involving electric bits are multiplied several times over.
Any self adhesive cover should be regarded as disposable - the glue only lasts so many re-applications and becomes a leak hazard. Have a look around, see what the racing lads use on their boats. Screw (or clip) down hatches will probably be good, but watch the weight, this boat does get a lot of its performance from not weighing much.
If it is the same radio that is used in the Dragon, there really isn't a lot wrong with it. The only problems that I found were the rather weak sticks and the smooth case of the transmitter, but Joysway have thoughtfully created a little hole in one corner to take a wrist strap or lanyard.
Trim? When it looks right, it probably is.
Are you wasting your time? In my opinion, no. In the opinion of serious people who think that any form of pleasure is a bad thing, yes. I think you last paragraph answers your question there.