This really did answer a lot of questions. What the prices Watanuki and Tsubasa(m) paid were for. It was so they could exist despite their parents' bodies disappearing. I now respect both of them even more; both want to have minimal impact with their existences, in their own ways.
No wonder the 'ending' was so abrupt... it wasn't really an ending at all. ^_^
It does suck some that Tsubasa(f) isn't coming with them, but at the same time, I'm ok with it and understand their reasonings. We got a confession for both couples now, and even Tsubasa(m) manning up at last and taking initiative.

I highly approve, hehe.
And yaaaaay for Kuro n Fai time.
I'm wondering now...... the "ending" is so open. For us fans, it's satisfying in that we can imagine any worlds we want for them to experience; their journey can continue in our hearts and our imaginations. That in itself is a great way for it to be.
But also, I'm feeling quite sure they'll pop up in the xxxHolic world at some point. Not guaranteed but quite sure.
And THEN.............. what if they show up in all of CLAMP's future works? What if these random world-travellers show up in Kobato? In any number of future stories as a mini-arc of seemingly random side characters? That'd be interesting.

Who knows? I won't go thinking it WILL happen, but that it might.
Guess we'll see what the future holds.
Thank you CLAMP, for a wonderful story, and for doing such justice to so many beloved characters. This ending is a great beginning.