You're right - as long as the barrel tenon, the depth of the chamber, the barrel extension and the torque of the extension onto the tenon are within spec... the headspace issue on AR-15's is largely a non-issue.
The only time I become concerned is when people put on their own barrel extensions. That's it, really. And that's because we gunsmiths usually "budget" about .002" for the "crush" of parts when threaded together under torque. On a bolt action rifle, we allow .002" for "crush" when we thread a barrel onto a receiver, and I allow/budget for that same .002" when I thread an extension onto a barrel for the first time and torque it to 150 ft-lbs.
Edit: I'd be spending the extra money on reloading gear. I suspect that if these idiots in Congress can't get what they want on weapons and magazine restrictions, they'll broaden their gaze and start hammering on ammo availability - eg, no more mail order ammo.