hey, great topic. I do this alot and believe it or not, i enjoy restoring old vehicles.
A little trick that i use tovget the crud out of tight spots and cracks is with a tiny flat headed screw driver and a lysol/clorox wipe. you wrap the wipe around the end of the screw driver (so it does not scratch anything) and give it a gentle scrub. I recently picked up a pretty scuzzy looking mobile command center that is 99% complete. took me hours of work, but it looks really good now.
If im replacing the decals anyway I will take the vehicle apart and just give it a nice hot soapy bath, and goo gone the rest. re-assemble and order more stickers from cobrastickers.com! presto, it looks like the day it came out of the box!