As professional radio engineer, what worries me slightly about this is that nobody knows if any particular GPS receiver is or is not radiating a signal that can cause interference. European limits are somewhat more exacting than US ones, but the possibility still exists. Screening of a/c systems is fine, provided that you can guarantee the integrity of the screening a few years down line, but there's been some published material showing that in fact, you just can't give that guarantee in practice. This is because cables chafe and move slightly, connections partially break, and cable screens get damaged.
Probably the worst possible case is the portable FM broadcast receiver on an aircraft: there has been a number of documented cases of interference from their local oscillators, which, in Europe, can run quite high levels and still meet the regulatory requirements under the EMC Directive (I haven't looked up the FCC limits). The problem here is that local oscillator radiation falls nicely into the band for the VOR.
When I was working on the systems design of GPS receivers (which was admittedly some 15 years ago), we certainly came across one design of architecture where the ability to radiate a signal in the VOR band from a local oscillator in a multiple conversion superhet receiver was there: it may well be that architectures have moved on since then, but I'm still somewhat dubious. You only need a clock radiating the allowed -57dBm in the VOR or comms band near a cable from the a/c antenna that has had some damage to the screening braid, and you could have problems.
After GPS, I was heavily involved with some Wireless LAN development: we had a problem in doing Type Approval because the brand new laptop PC from well known Far Eastern manufacturer radiated so much rubbish so far outside the limits allowed that it failed our WLAN! And the manufacturer of the PC didn't want to know......so I'm a bit dubious about presuming that just because it's a type approved, CE or FCC or whatever marked equipment, that it's OK.
Just because you've got away with it so far doesn't mean you can be sure of carrying on doing that - it's a bit like visiting a brothel and taking no precautions. You may not catch anything this time, but keep going back and sooner or later........