The philosophy down here is buy better glass before upgrading the body.That's a leftover from the film era, when the body was mostly a light-tight box for your lenses and for your sensor (film), and no one caring about quality were shooting APS.
Now, an FF body will make your L lenses work better.
I still agree with the sentiment... for 2 reasons... Lenses don't depreciate quickly... so you are better off running your body into the ground (150K of actuations) because it won't really be worth that much after a few years when you try and sell it. Point in case... the 1d iii which sold for $6K and is now selling for $1k. Whereas... if you bought a few nice lenses, you can still get well more than 16% of their original value.
And you can put an L lens on an older body and still get fantastic results... depending on what you are shooting. If it is landscape or portraiture, the advances in high iso performance and AF performance are minimized and you can still get some amazing images using an older XTi. Heck... if you are still rocking the t2i, there haven't really been that many advances along the lines of the crop sensors that would warrant buying a t5i.
When I sold my XS... it was a wash... when I sold my 60D, I lost $200 in depreciation... and when I sell my 5D mkiii, I will lose around $1000 in depreciation... which kills me. But maybe I avoid that by just using the mkiii until it dies in 10 years.
If you can throw $10'000 on glass, but you cannot justify spending more than $500 on a body, then you are being unreasonable. APSC sensors are only using 40% of the L glass potential. Even if you only got 3 or 4 lenses and use them / love them equally, then each one will only get a quarter of your attention, while the body is used for 100% of the time. If you worry so much about the resale value, then why not buying used bodies? I'm sure about one thing - I should have bought a used 5D with 50/1.8'II instead of a Rebel with some zooms (for the same price). Yes, I'm not one of those "covering the range" people.
I think that there is a conflict between two topics - "lenses before body" and "FF vs Crop" - which shouldn't be merged. However, when they do merge we get "$10'000 of L before FF" which sounds like "marriage without sex", or "FF with only $8000 of L" which sounds like fun (and the right way to do it), or "FF before any L" which sounds like "sex before marriage" (kinda fun too , for a hobby).