Having only room for 3 machines myself, and also owning two of the 3 (TZ and Indy) games on your wishlist, I figured I'd offer up my two cents. I would definitely consider two main factors in your quest for a second machine: your budget and game variety.
Budget:
The games you've listed are all potentially great options, but they vary quite a bit in price. Indy and TZ are the most expensive at around $6000-$8000 (Indy tops out higher than TZ), then Addams ($5000-$6500), then Whitewater ($3500-$4500), shadow and no good gofers ($3000-$4000), and finally Dirty Harry which can be had fairly cheap ($2750-$3000).
Game variety:
Getaway is a fun game, but it's fairly shallow from a depth (ruleset, variety of shots, code) perspective. I'd definitely recommend a deeper and potentially more challenging game as your #2. You definitely want something that will hold your interest and will simply feel like a different experience from the getaway. Personally, the shadow is a tough and unique game and goes for a lot less than some of the others you've listed...people seem to love it (I would like to own one at some point) and it's definitely challenging. To me, whitewater is a bit shallow as well, especially for how much they're going for these days. It definitely has more complexity than getaway, but the shot selection isn't all that varied.
Hopefully that helps ya.