Why cripple your projects? - use whatever is best at the time.
Who mentioned I2C?, I2C can be slower than SPI, but it has many advantages over it as well - and for running a small low resolution mono display either is more than fast enough, in fact I've taken to using the slow software SPI on my 5510's because there's no advantage using the far faster hardware.
GPS modules are simply serial ports, and you connect it to the PIC serial port (or any I/O if you use software serial) - it's hardly a 'protocol'
The one I posted is in colour though, and has greater resolution - just in case you had greater ambitions.