I'm stuck on this minor issue of what wheel to run for 'cross racing/trail riding. I have a set of Mavic Ksyrium Elites and I also have a set of handbuilt Mavic Reflex tubies laced to Record Hubs.

I am leaning towards running the Reflex/Records because they are #1 lighter, and #2 sew-ups, so I can run a little lower pressure and get more traction when the course calls for it. and #3 use standard spokes found at any LBS if I break one.This is an either/or decision because one set has to go to a friend, I just don't know what set.

Sounds like you made the right choice. That said, I think it's nice to have a set of tubular and a set of clincher rims for cross racing. You especially don't need the tubulars for trail riding, so I guess it comes down to how much racing vs. trail riding you expect to be doing. As they say, my .02.

It's a matter of prioritization, I'd say.

As nice as it is to have a nice set of tubulars for racing, they certainly aren't very practical off the race course. Personally, I'd probably keep the clinchers for now, and just plan on saving up for a set of tubies by next fall.

when you can usually buy 2 sets of tub wheels for the price of one set of K's?

I run Tufo T-34s on my beater, trail riding tubular wheelset. also good for when courses are far more rocky.