What I'm going to first is just think about some of the components. I'm ignoring all the sensors here which wil get added as we progress.
In terms of the display what I have lying around is a pair of MyVu Solo Plus video display glasses. I think mine were from e-bay for about £35. It is definitely possible to pull the LCDs out of these glasses because it's been done on Hack a Day. For now I'm going to leave the LCDs inside the MyVu though.
Edit: also found this on instructables (http://www.instructables.com/id/Raspberry-Pi-wearable-computer), which is encouraging to see the idea isn't completely daft.
For processing data, running the display etc. I think I'm going to use a Raspberry Pi (at least for now). It will output composite display, which is what the MyVu wants. It should also be very easy to program, and allow connection of other sensors. In addition to the Pi, as standard I tend to get an Edimax Nano USB Wifi dongle, just becasue it makes interaction with the Pi easier (mine was from Amazon).