Not close at all. I have a couple of upscaling DVD players and the image quality difference between 480p/720p/1080i is barely perceptable. It mostly depends on whether the scaler in the DVD player is better or worse than the one in the TV.
Remember that no matter what the resolution you feed an lcd, plasma, or dlp based tv or projector, the display will scale to it's native resolution since it has a fixed number of pixels. So feeding a 1080i or 1080p signal to a display that has only 768 or 480 scanlines will result in it being downscaled again anyway.
For standard DVD, the key thing is the quality of the deinterlacer and even the output devices. I would generally stick to the better players like the before mentioned Oppo, the Panasonic S-97/S-77, or the better Denon models.
The other option is to use your PC, the quality of the deinterlacer available with an ATI x1000 series is supposed to surpase even the best standalone DVD players. Check out the article on firingsquad.com where they covered that; at the end of last year ATI released with their cat drivers an update that greatly improved their deinterlacing. It would also give you a chance to see how much of a difference that upscaling makes.