I don't think there is anything wrong in taking a persons idea and developing it further. If they didn't Superman would have died with Siegel and Shuster. Sherlock Holmes would be confined to a few books in a dusty library. Its all the same. It takes equal creativity to take a two dimensional group of characters and update them. Some of the old characters only had an image, a motive and a name. Why not bring them back and flesh them out? It needs to strike a balance between new and old because old will run out. The next generation of writers will need their obscure villains too.