Please bear in mind that higher resolutions only benefit screens that can handle it.
My Panasonic plasma TH42PWD6EX (3 years old now and still shining) has not got enough pixels to handle more than 576p (PAL).
So there''s no improvement when dialing 1080p in DVI mode, which is calculated down inside the Plasma.
Still, 720p gives a slight improvement over 480/576.
That said, a good scaler beats any DVD's picture quality and tweaking options.
I am VERY happy with my DVDO, and I just noted they do reconditioned units of the HD+ around
$500, so if you don't need HD go for it...
Lenexpo als offers DVDO units http://www.lenexpo-electronics.com/