Ah, the old scaling debate...
This will probably never end because upscaling is such a good marketing buzz word. Here is the skinny on upscaling. Basically, you should not be overly concerned with scaling. For most content, I turn off all upscaling features of my average electronics and let the good scaler in the TV handle the scaling. Your TV has a fixed resolution, and any content that is fed to the TV will be scaled to fit that resolution. In order to do this, the TV has a built in scaler that converts a DVD at 480i to 1080p of your TV. If you pass it a 720p or 1080i you TV scales it to your 1080p resolution. Most quality TVs do a pretty damn good job at this. Your average "upscaling" DVD player does a pretty average job at upscaling, and chances are your TV still scales the image again to fit its exact resolution. You Oppo is a good player, so it may match your TVs scaling, but unless you buy a high end product with a proven scaler in it like a HQV Reon chip in the Onkyo 875, you will see no differernce in scaling and your TV may actually do a better job. So, moral of the story, don't buy source equipment for it's scaling ability, buy your TV for it.
For scaling, the important step is in the deinterlacing and the scaling is easy. For that all you need is a good progressive scan DVD player