Thank you all for the great advice! Looks like the road ahead will use the new XBee-Arduino API Library, with draythomp's tutorials as a reference point, the new COSM library (updated since 1.0.3) and my MegaADK as the Base Station.
I'll post the results here once I get it working, and (not to get ahead of myself...) I'll also post results of any further experiments combining different Arduino boards with XBee or with Raspberry Pi/OpenWRT. I finally got the serial header working on my Asus WL-520gu router running OpenWRT last night, so I might just end up converting that to my base station.
But first things first I guess its time to get over my aversion to API mode!
Thanks Again!