GPS does have a group that protects it's users - I believe it's called the USAF.
So there are enforcement people out there. They just don't happen in the middle of a superbowl broadcast.
They unfortunately do not have nearly enough officers to really do anything particularly effective, but if you are really egregiously bad about your spectrum abuse, to the point where you generate complaints from other users, they do sometimes pull licenses.
The only interaction with them I have any sort of knowledge of is secondhand; a friend of mine spent months trying to get the local power company to fix a bad transformer on the street that was failing internally and creating a lot of noise, pretty much from DC well up into the HF. (And I suspect it was making some pretty ugly AC waveforms.) They wouldn't do anything, and he eventually got one of the FCC Enforcement Bureau people involved.
You have to be a very "squeaky wheel" to get any sort of attention to a complaint, though; my friend had what amounted to a fairly serious engineering study of the failing transformer, done with parabolic antennas and spectrum analyzers, so that the FCC guy didn't really have to do a whole lot. (Presumably he verified things, but I don't know for sure.)
Using two frequencies makes the military receivers more robust, and also lets them do some clever ionospheric distortion cancellation that you can't do with one channel. (Basically they get the benefits of WAAS without actually needing to receive the WAAS signal.)
That said, neither the FAA or the military are going to tolerate any significant degradation of GPS, domestically or otherwise.
BTW, I'm not a pilot, but I work for a government aerospace contractor, so I have some experience in this.
Since this thread sprung up I've wondered what might be impacted by a GPS failure.
As far as BIS info, it's not something I've followed closely, but we're talking things like every plane, tank, and infantryman now (soon?) has gps and information on the location of all friendly forces is automatically shared so you cut down friendly fire.
Apparently caf has more info on milspec GPS than I do, I thought that it required the same main band as civilian, and just used additional military bands to increase precision, but apparently it can function fully independently (not really surprising when you think about it). At least that gives you a little info on some of the troubles of failure of military GPS, as unlikely as that is.
This specific problem definitely wouldn't affect our aircraft simply because they would be at such a high altitude. Even if it was a problem, the military also has a some pretty impressive anti-jamming capability.