As an ergo user, I'm happy to throw in a few extra 1.5u mods as needed. My ergo layout doesn't call for 2u vertical mods, but if we're only a few away from making MOQ on those, I'm happy to throw in those as well. 2u spacebars for the vertical mods definitely makes sense in terms of reaching MOQ; however, as far as use, I don't have experience using 2u spacebars because of what I mentioned above.
Also, let me throw in a plug for N9 (dark grey) keys. A lot of sets use them. GMK SkIIdata, GMK Nines, GMK 9009, GMK Terminal, a few others and also the most recent one on Massdrop incorporates it as well, GMK Eclipse. I've also noticed that the dark grey from Carbon is not too far off N9. But the white and black of CR and WS1 definitely make sense too if you are needing keys to match other sets.