I agree with your ideas about captured junk, although I might add in being able to reverse engineer them into buildable unit designs. Yes, I know this has been discussed and dismissed, because "noone ever really did it" BS maybe it doesn't happen much these days but it used to be the rule of thumb to destroy your plane if shot down over enemy territory etc.etc.etc. If a USAF pilot screwed up and landed an F-117 or B-2 in Iran...they would be building copies... it might take them awhile to get the right materials...but their science would get a boost from it. They WOULDN'T simply park it at an airbase and use the single plane for airstrikes. I'm thinking that if a unit has prerequisite techs to learn before you can build it, then you get the option to study those techs and eventual availability of apropriate units... tack on a short "tech invention" called reverse engineer, to make the prerequisites open, and the unit is not usable for combat afterwards.
Also, Ains, Whoever said you couldn't amphib assault both coasts of panama at one time?