If the next body had very clean very High ISO files..Id upgrade....if it were just better AF..I wouldn't..
I still think there's plenty of room for cleaner High ISO files..so Id say most would upgrade just for that.
one observation I have on DSLR's over SLR's is the assumption that he new media {digital } is cheaper over the older media { flim} as there are now no processing costs.
Id have to disagree....what we have now is the need to dump a body if a newer better one comes out...in film, we just bought a new roll with better ISO capabilities .
also now we have thousands of redundant images that don't get deleted { in my case}..whereas we just did a roll of 36 and called that it for the afternoon..LOL
but I digress
my first body was a canon Eos 750..went to a Eos 650..then back tracked to a Minolta X700 Manual...which I still have and love...I just dont shoot with it anymore