As for frequency conflicts driving a switchover to 2.4........... When you've got a number of good RXs in good airplanes, the changeover is going to cost big bucks. And you will notice that lots of your club members are no longer going to be conflicting with your frequency because they're on 2.4 now. Good for them. Good for us guys with lots invested in perfectly good RXs. A TX upgrade may or may not be worth considering. After you're back in awhile, that question will answer itself for you.

As for your engines....... If they're gummed solid, you might consider buying a crock pot. New ones are under $10. There is a new deal technique of cleaning up engines that amounts to crockpotting them in antifreeze. It works wonders. I had a number of engines when I got back into flying a couple of years back. Had a number of engines with 15 years gumming up to clean up. The crock pot does the job overnight. Well worth it.

Swap out all the battery packs. Including in the TX. I took the opportunity to standardize the packs in all the planes. Went to 800mAh packs in all. Got my charger setup for 4cell/800mAh and no question about setting it differently for any airplane. NiCd works like a charm still.