From what I've read, Soul Calibur (XBLA) really has nothing to offer those who already have Soul Calibur (DC).
The graphics are the same, so there's no positive there.
There's no online play, so there's no positive there.
The mission mode is gone, so there's a negative there.
There are are achievements and a leaderboard, so there are two positives.
But in your opinion, are these two things worth the $10?