Bronze Grayskull is one of three figures that keeps me from saying that I have a 100% complete collection, technically speaking. I'm also missing the original SDCC version, as well as color-changing Orko. I only have the regular Matty re-issue of KG with the orb of power.
Still, I don't feel that the Bronze KG is worth the current prices. I'm a loose collector, though, so I'm happy enough with the regular KG I have. If I have my info straight, the SDCC version is the exact same figure with a slightly different paint deco, particularly on the cape. I might pick one up at some point if I find a good deal on him but the bronze version is usually too expensive. He's practically priced the same as Castle Grayskull itself, which is way too much for a single MOTUC figure IMO.
If I really want a statue of KG, I could repaint a re-issue of him instead and save myself a lot of money. That's just me, though...Bronze KG does look neat and I can understand how some would feel that their collections would be incomplete without him.