If you plan on doing everything yourself, go with Avid Liquid 7. It has more features than XPro does, including secondary color-correction, timewarp, 3D warping, masking, surround sound, etc. Very powerful application.
If you plan on working with other people in post (“collaboration”), such as finishing on a higher-end Avid, working with compositors, audio folks, effects artists, color-graders, etc., then DEFINITELY go with XPro.
XPro offers many more features than XDV and is WELL WORTH the extra money!!! For starters, as of XPro 5.5 due this summer (target date is June), you will have the full Avid Film Composer toolset…the exact same toolset that most Hollywood films are cut with, that, up until now, used to cost $25,000 to get via an Avid Media Composer Adrenaline system. It cost even more back in the old Meridien days! I realize you said you won’t be outputting to film, but this is huge in and of itself.
Other improvements over XDV include 3D effects, HD support, 24p support, Marquee Title Tool (far better than the standard Avid Title Tool), multi-cam (4-streams of RT), Timewarp FX presets (canned, can’t be tweaked, but better than nothing).
It goes deeper: XPro offers support for Mojo, which allows you to work with uncompressed video…meaning BETTER RESOLUTION and higher-quality output. You can work with more resolutions, too, including 15:1s offline for your rough-cut to save disk space.
This is but merely scratching the surface!
Also, XDV’s future is extremely uncertain, and looks as though it’s going to be killed. You might as well spend the extra money and get a product that is going to continue to see a healthy life as it gets upgraded and improved constantly.