Hey,
I'm working on a TMNT one right now, it's in project announcements (shell shocked) but honestly do whatever you think is going to look cool, and that YOU will be happy with. Honestly who cares if someone else has the same thing. To me the biggest reward, has been building this thing and watching it come together. Some people have a knack for building themes that work and I say take advantage of that... All the artwork I have is from all over the place, and took me days to collect and get together. and I went through all kinds of ideas, Star Wars, with a light saber done up with a neon bulb would be cool, X-men with Cyclops' visor light up, Transformers and Thundercats were also on my list, or Silver Hawks.
Ultimately I went with TMNT because one it was a game I really really liked and enjoyed, two it was a 4-player game, and I wanted a 4-player control panel and three, the poster I had to get done up as the artwork I though would look awesome. At the end of the day if you make your cabinet and down the road you find someone has something similar is it going to mean you