My advice would be to just stick with what you have for the time being. The differences between DSLR and 35mm resolution might be slight , but there are huge differences in the capacity to record subtle tonal differences, especially as you get down toward the darker end of your tonal range. If you have to sell something to advance your photo pursuits, I'd say sell a lens or two to buy some darkroom equipment and spend the next year or so learning how to get the best black and white images you can out of your 35mm camera. I don't think you'll regret doing so, and you'll be better equipped at the end of that year to know into which basket you want to put your eggs.

-KwM-