I have to agree with the question regarding the value of an Oppo for those not interested in other multi-channel audio disk capability.
Upscaling would probably be the best reason, but the latest Panasonics are quite good (like my BD55). I guess if your share of DVD viewing is quite large compared to BD, it might be worth it.
Also, I think the dedicated 2ch CD sound from the Oppo is superior.
I like the use of 80Hz xover vs. 100Hz bass management in the Panasonic (and many others..in fact Pioneer uses 120Hz) as my receiver does not process HDMI audio. Although, even the Oppo BM setup has a couple of limitations as pointed out, though likely minor for most.