It would only have a Huge boost in Japan. Correct me if I'm wrong, but I don't think any JRPG has give the 360 a huge HW boost in the west. SW-wise it would do 1-1.5m max looking at other JRPGS (TOV, SO4)
Are you REALLy comparing DQ to ToV and SO4?
In Japan DQ is King and it would give 360 one hell of a boost. 2Mil minimun for DQ on 360.