I think it's all in the presentation and execution.
Castle Greyhawk for the Grognards. A whole new world to explore for the newer faces. Populate with different and interesting stuff, like portals to weird lands, and have different things like the 9 imprisoned Gods that the PCs have to interact with in interesting ways - it could work.
I mean, just about everything has been done, including tons of takes on Greyhawk itself.
The trick is to do it in a fun, new way that appeals to the old and new crowd - which I think is your whole point, No?