Are any of the very old Canon full-frame DSLRs worth buying?

When the price is right I am going for a 1dsmk2.  I currently use a 5d and happy with image quality and landscapes, but I want another 1d series  ergonomics to go with my 1dmk2.

You should handle any 1-series and see if you like it, personally I do.  You may have to budget for a new battery if you go for an older camera though.  Fred Miranda web site is a great place to read user opinions on these cams.  Tom