It's a matter of whether you can live without the latest features and gadgets in the end... The Sony has built in image stabilisation, dust control, more pixels, live view, a big review screen etc - the D2 doesn't... By the sound of it you are coming from an earlier era so probably could easily live without the latest all singing whistles and bells.

My first DSLR (indeed my first digital camera!) was a Canon EOS D30 bought second hand. It was something of an impulse purchase as used DSLR's were extremely rare at the time and it was more a matter of grab it while it was available than a rationalised decision - I was essentially a Nikon manual camera user at the time. My second DSLR, this time a 20D, was also purchased used though this time I had been on the lookout for an upgrade. At the time the 30D (not to be confused with the earlier D30...) had only just been released and was well outside my budget so I got a lot of camera for a lot less than I might otherwise have had to spend. Since then the pace of 'improvement' has rocketed and prices have tumbled so the advantages of an older, slightly less advanced, model relative to price aren't quite as clear cut.

As to using an older camera? It's fair to say that the performance, overall, of more recent models is generally better than older cameras - particularly at the extremes. High ISO and faster frame rates spring to mind as examples but are not the be all and end all of things. Pro cameras for instance may well have faster and more accurate AF than a more recent but budget camera (you only get what you pay for and speed and accuracy costs).

I still regularly use my D30 and even at extreme ISO (a recent ISO1600 example here) but there's no doubt that the 20D is a bit better noise wise (image noise anyway, the mirror noise is way worse). I'll probably stop using the D30 when it gives up the ghost (it's worth very little these days) but until then it's likely to take many more pictures...

Guess I've waffled on a bit but maybe it's helped...