I would keep them all and use each one for its specific purpose. What I mean is, although the Sony will write CDs, it seems a bit of a waste of its capabilities and it will wear more if you use it for that. Likewise with DVD playback.
I don't have a DVD writer in my current machine but I do have a CDRW, a CD ROM and a DVD ROM and each gets used for its prime purpose and nothing else. When I do get a Sony DRU, it will be an addition to, not a replacement for, the others.