However there is a problem with both ideas:
If we're leaving wrecks on heavily AI controlled planets (say, at the foot of a Mark 3 fortress) it would be impossible to recover those units/resources until after a refleet and a stomping all over the place that killed the originals. So it doesn't wholly solve the problem, just shifts it around some.
Well, I trying to not give the player free resources for nothing here.
Suicide your entire fleet into a Mk III fort? Ya, those resources are gone.
Botch an attack for some reason and realize you need to run away but don't make it out? Or even know you are not going to make it out so you send your fleet off to the edge of the system. Those wrecks should be reasonably easy to recover, and doable with a small number of units that while waiting for your refleet you can be occupied recovering wrecks.
One important caveat to how I envision this working is that if you've lost your
entire fleet, you've screwed up badly somewhere and are now paying for it. I'm concerned with the late-game rebuilding of super-weapons here that bankrupt your economy.
After all, if you are going to use a unit, you accept the possibility of losing that unit.
Hmm, salvage sounds interesting, particularly if you can also salvage AI wrecks ("that's not a chokepoint, that's a chop-shop"). It could finally be a purpose for the vestigial Cleanup Drone 
And their FRD logic could probably take care of it without your needing to do much.
My main concerns:
1) Is that actually fun?
I think just about anything would be better then what currently happens during a rebuild. My most common activity is punching scouts farther out during that down time, but once I've got the entire map scouted I'm sitting there twiddling my thumbs.
Note that I'm using rebuild in the sense of it's a relatively short down time. I simply don't do attacks where I lose my entire fleet so at worst, I'm rebuilding maybe half my fleet and what I've got left is still capable of launching attacks against weaker targets.
If it's a situation where the only way I could attack would result in losing my entire fleet, I break the warheads out. (And yes, I've the full cap of 18 lighting warheads at a 10,000 unit CPA before, still lost the game but the loss was not due to the warhead AIP.)
2) Does it actually address the refleeting issue?
I think so. It gives you something to do that has a purpose as the better you are at recovering wrecks, the less time your refleet takes.
3) That's a lot of wrecks, so RAM may not thank you. Though we've optimized the "remains" thing pretty well. And if it's only the bigger stuff that leaves wrecks (as humorous as youngling wrecks could be) that wouldn't be too bad. And the wrecks could just disappear if not cleaned up for 30 minutes.
Bear in mind that graphically it would just be some kind of generic debris; doing wrecked textures for a bunch of ship types isn't in the cards
Certainly it would be the bigger stuff only. A wreck that only gets you 500 resources back is pretty pointless.
Also, when looking only at fleet ships, the current resource cap does feel right. It's when we get into super-weapons that the cap feels small, and recovering wrecks is effectively a resource cap increase when using superweapons without actually increasing the resource cap.
D.
edit: I just realized there is one big variable we've missed. Multi-HW starts.
I play "small" games with a single-HW and most super-weapons turned off and most of the time the current cap is fine for me.
However, a 4-HW start losing half it's fleet is (roughly) 4 times the resources to rebuild that losing half my single-HW fleet would be, but the resource cap stays the same.
I could support a scaling resource cap for multi-HW starts, maybe an extra 300,000 each of metal/crystal for each additional planet?
Multi-HW start has other offsetting advantages (notably more resource income) so this resource cap increase does need to have diminishing returns.
D.
