Great topic, I've always this wondered myself.  I'm just like you...saving everything I'm earning from stock to put towards a DSLR.  I'm getting decent sales selling almost everything at 3.9 mp through Dreamstime.  It's good by my point of view, since I only got into stock photography in mid-December.  I've got a good camera, but I'm craving more.  You have some great stuff in your portfolio, just stick with it and eventually you'll have some people buying your work.