I might also add the "halos" or whatever you are using as a border for your action buttons for the trackball and admin buttons so everything is uniform.
Also, in regards to the 4P set-up, a lot of people (myself included) do not like them. Well, it's not that I don't like it, I just think it is overkill and won't get used as much as you think it will. Also, there are only a handful of games (10 maybe?) that support 4P and they are mostly clones of each other. Of course, I'm not counting console emulation in which case there may be more games but for those you could always rig up some controller ports for the extra players. I don't know... it is expensive, large and might not get as much use as you think it will (I'm lucky to get a 2P game going in my house other than the few times a year we have a party). I don't think the benefits outweigh those things.
At the end of the day though you have to do what makes you happy - there are some KILLER 4P setups around here so it can definitely be done. Just be sure it is for you - I have a 4P setup on my cocktail table and I HATE it. I can't wait to take a saw to the long CP. 
Doing a search on maws.mameworld.info/maws, it shows roughly 100 4 player simultaneous games that aren't clones or bad dumps.
I like the idea of having a few of my friends over and us all playing. Room isn't an issue for me, the extra expense of 4 players is only ~$100, which is only the cost of a good trackball.
Maybe I'm learning the hard way? But I don't see any major advantages of shrinking the CP.
Don't think I don't appropriate your advice though. I love the cabinets you've built.
This is my first cabinet build, with no experience and little woodworking skills.
...crossing fingers....
