Banjo, although I got much useful service out of my Vista HCx and there is an incredibly large fan club on here and other cycling forums, I wouldn't buy a eTrex Vista now. Unless you get a really good offer or some kind person on here or elsewhere. I've listed some of the important specs. I believe that you can see that the eTrex 10 is really a replacement for the very basic garmin eTrex H. If you did buy one of the old eTrexes sure they are very rugged and even with the 'limitations' of 256 colours (C means colour in the letters) they are useful.
eTrex Vista HCx
256 colours
display 3.3x4.3cm and 176x220 pixels
20 saved tracks
no built in memory
microSD slot
barometric altimeter
eTrex 10 vs eTrex H
monochrome vs monochrome
128x160 pixels vs 64x128
basemap only vs not even basemap on the H
no built in memory in either
no microSD slot in either
100 saved tracks vs 10 saved tracks
no barometric altimeter
garmin connect (the H doesn't even use USB let alone connect)
The 10 also has GLONASS which for some of the people who might have used the H for particular things (let alone the original basic etrex with no letters after its name) would be a fairly big advantage to put it mildly.
eTrex 20
65k colours
176x220 pixels
1.7GB inbuilt memory
microSD slot
200 saved tracks
no barometric altimeter
garmin connect
GLONASS