Welcome to the Netduino community!
As long as the shields use different pins and are "stackable", you'll be fine. Stackable shields have pin headers on top which match the layout of the Netduino.
Also, GPS drivers should be easy--but you may need to write an interface for the Wifly shield. You'll also want to make sure that it's compatible with 3.3V signals. Netduino can take 5V--but it's an ARM board so it only outputs 3.3V.
Thanks for the reply.