I'm seeing stand-alone GPSDO 10 Mhz source prices falling; if I use an external, non-Flex, GPS referenced 10 Mhz oscillator, do I still get all the other good stuff? (time, grid square, elevation, speed, etc...)
No - the only thing you will get is the stability and accuracy of the GPS source used to lock the internal frequency reference.
The other information requires the internal GPS - the external GPS unit has no way to provide the other information which is output as a data stream from the GPSDO independently from the frequency reference.
Sorry - no free lunch for the GPS reference information!