I believe that you made the right decision. I do not think that there is much difference between the D40x and the D3000.
I had the D40, which I really liked, but upgraded to the D300. This was the main reason for it:
The above photo was taken with the D40 + 18-70. I just could not crop anymore without major loss in resolution. I never had that problem with the D300 and the D5000 has almost the same sensor. I just came full-circle sold the D300 (I have the D700, though) and got the D5000 and could not be happier with it. It is a fantastic camera, small, quiet (on quiet mode) and very powerful. For street shooting, it is tops, imho.