Warren,
I, too, used to do the CMN telethon. One of the best!!
Digibeta is a great mastering format and a DVW-A500 will play back Betacam and Beta SP tapes (a DVW-500 will not). Look for the Analog/Digital print below the tape door. Neither model will record to Beta SP. You can shoot on D-Beta as well, but either DVC or D-Beta will give you great pictures.
As far as editing on a DVCPro, the trajectories (speed) of the cue buttons on a DVCPro deck are much different from any other braodcast-quality tape source. It will take a lot of getting used to. It is also difficult to scrub audio for accurate audio edits (using a CMX).
Hope this helps.