Wow, wish I could have a space like that.
Here are a few comments, feel free to ignore them if you don't find them useful...
1) It's unclear from your diagram if the yellow area around the pool table is a wall or not. If it is a wall, then you don't really have room to play the pinballs in the top row. If it's NOT a wall then people can't play those machines (safely) while someone is playing darts. Why not move the darts to the north of the pool table - for safety sake.
2) Consider having the door to the office open the other way (into the hallway). It will give the office extra space without really losing anything.
3) If the spiral staircase is the real entrance to the space (and the straight staircase is for loading/unloading), maybe you should consider making this a ramp instead of stairs. It would make loading easier and might then make the space wheel-chair friendlier.
4) If you really plan on having 20 or more pinballs, you might want to consider a workshop type area for repairs, etc. If you have 20 machines, there will always be one or two that need some work. Having a place for that would be nice - I don't know what work space area you already have, but even if you have a nice garage workspace, moving machines back and forth would suck.
5) Is the "hallway" that leads to the home theatre there for sound dampening and/or light shielding? If not, it seems to take up a lot of space. Maybe there is a better way to use this space without losing anything.
6) Replace spiral staircase with "bat-pole".
