Let's take a look at the Constellation:
Aside from the crispy-critter warp nacelles, the ship really doesn't look to be in particularly bad shape, especially when you consider that the design is pretty modular in arrangement. New bridge, nacelles, pylons, some systems repairs and upgrades, and about six months worth of spacedock time patching up the obvious structural damage, and she'd be back in service.
The E-D saucer section, on the other hand, is large enough that it could probably comfortably contain the Constellation, and has already been determined by her designers that, under standard Earth gravity, she would sag under her own weight if not for some serious reinforcement by the structural integrity fields.
Take that baby and bellyflop it onto the surface of a Class M planet, while skipping more than a few steps listed in the tech manual, mix in the detail that the aforementioned SIF is gonna go out at some point, and you get one very large unsalvageable structure. Even if it survived the crash landing (emphaiss on "crash"), it likely wouldn't stand the strain of being lifted up by tractor beam.
And if you had a transporter large enough to beam up the saucer section of a Galaxy class starship, well, you wouldn't need a Galaxy class starship in the first place, now would you?
