Because I am a confessed spendthrift, a few days after my original post I ordered and paid for the Eagle XX1 drive train (minus the cranks). I had it installed on Sunday. Because of weather and time constraints, I've only ridden it 15 miles so far. I noticed immediately that shifting into the smallest cog was clunky and slow or didn't happen at all, so I had to learn how to set the high limit and index the gears (a good experience). Its fine now.
Does it seem worth the extravagant price ? So far I would say it is not. I hope this will change as better weather allows me to ride more challenging terrain. My immediate feeling is, as Rob said... "It's all marginal gains and maximum cash loss". I have forgiven myself and will enjoy it nonetheless ?