If you can get hold of a hypodermic needle, getting rid of dings in balsa (under the covering) is real easy. Use the needle to inject water into the dent in a number of spots, then heat it with a covering iron. The water will flash to steam and the wood will swell and level out. Works great, it's cheap, it's easy!

Grimy engines.... Go to Walmart and spend $6 to $8 on a small crockpot. Fill it with antifreeze (not the bio friendly stuff), remove rubber and plastic parts from the engine (like carb "O" ring) and put it in the antifreeze on low for about 4 hours. Scrub it lightly with a toothbrush under warm water and it'll shine.

Protecting wings? Be more careful (or less fussy).
Dennis-