I think it all depends on how serious you are about photography. There's a big rule that I'm slowly but surely learning about photography, and that's that spectacular photos are much more from the eye of the photographer than they are from any piece of equipment. One of the best photos I've ever taken was with a $19.95 piece of junk point-and-shoot film camera. That doesn't mean I don't get great shots with the setup I have now, it just means that it's not
necessary.
If you want to veer more towards a certain aspect of photography, say sports photography, then yes, you might want to consider getting a professional grade camera that can support a variety of interchangable lenses. Likewise if you want to start shooting weddings (need to be able to use a big off-camera flash unit) or studio work (need to be able to control slave units and such).
Me personally? I'm in love with my $600 Minolta DiMage 7i. Sure, I'd kill to have a $4000 D-SLR, but I know that 1) my budget won't support it, 2) my wife wouldn't let me, and 3) at the moment I don't do the types of photography that would fully utilize that sort of equipment.
Anyway, not trying to talk you down from the ledge or anything--If you've got the resources and are 'into' photography enough that you could make use of a D-SLR, friggin' go for it and never look back at the rest of us peons!
But if your camera is not glued to your hand and you're happy with the shots you get out of your present setup(s), work on developing your eye instead of your equipment bag.