Does anyone know when the next big thing in gps is coming out? A navi GT51 perhaps? How about a bigger colour screen with Realspeed functionality built in to the firmware. It would be great if it could calculate alphas on the fly, or show us on the map where we've cracked out top 2 sec peak, with speed coloured tracks. Maybe this could be incorporated in the GT 31's firmware.
Just thinking out loud - I need a new Navi, and I know as soon as I plonk down the cash for a GT31, the GT51 will be released.
I don't think there is much likelihood of the GT-51 coming out anytime soon. Locosys made a few prototype GT-35's with both a 5 hz MTK chip and a Standard SirF 3 chip but they didn't like the economics enough to put it into production.
I have one of the protos and I can say it does not seem to have any significant advantage over the GT-31 for most normal uses.
A new case design would be nice if it could be more waterproof but I don't think anything is on the drawing boards there either.
There have been rumors of other brands building something specifically orientated towards GPS-SS but nothing has come of it yet. I think it would take a year or two even if they are full steam ahead and then it would take a while to test and asses it for accuracy and reliability.
I think you are pretty safe to get a new GT-31. 
