I'm not sure exactly what would be the magic number for a safe amount of down travel. My thought is that this is somewhat of a grey area. If we knew this, we could definitely do some testing to see how the various setups line up.
You've got to remember that while 1" seems like a huge difference, in actuality the coil is only compressed 1/2" more. When I had my Bilstein's, I moved them from the second notch (.85") to the third notch (1.75") and didn't really notice any difference in the ride.
However, you've really got me rethinking this. I know I've read comments where people are saying the can speed up for speed bumps and it still glides right over. Mine does well, but not well enough that I can make that comment. I'm thinking adding a spacer and having less preload on the coil may help here. I cross 15 speed bumps daily, so if this (among other areas) could be improved by adding a spacer and reducing preload, then it's well worth it IMO.
The only complaint I have with the OW front coil overs is that there's a noticeable clunk. At first I thought it was something loose during the install, so I went back over everything I could think of in the front suspension and retorqed to factory specs. The noise was still there, so I e-mailed OW and was told this is normal. I've also read where others have experienced this. It's not all the time, just over certain bumps you'll here the clunk.
I would really like to use the Daystar budget boost front spacer (approx 2" lift) but I'm afraid it would be too much. I'm really considering adding the Toytec 1" net lift spacers to the front. As you pointed out, there is seemingly a ton of benefits and not a lot of proof that there are any cons to the setup. Other than what I posted from the conversation I had with Andries, the other stuff is pure speculation on my part. I agree 100% with your thoughts. I guess the deciding factor would be if we could somehow determine a measurement of the maximum safe amount of droop, until then it's a guessing game.