I'm a bit out of the loop, having quit when the Mumbad cycle was announced.

But the Revised Core Set has sparked my interest. Does it 'only' contain a different mix of cards or does it also contain some 'revised' cards?

None of the cards are mechanically changed from their original versions, but some have new art. If you had the complete Genesis and Spin Cycle and two Core Sets then I’m pretty sure you don’t have to buy anything unless you want the shiny new art.

That's good news, thanks!