There's decent reasons why the "HD" broadcasts of TNG look better than their original broadcasts it's because Videotape still has, fairly, high reslution to it, infact in the best of circumstances its resolution can almost reach DVD's resolution. (This is the resolution for the type of videotape used on productions like TNG, not the necessairily the resolution of the videotapes you'd buy at the local store.) But it cannot reach HDTV's resolution which is at least 740 lines of resolution. Videotape, even the quality of videotape used in productions (especially production done in the early 90s) cannot achieve this.
So just because TNG is on an HD station doesn't mean the content itself is in HD. It's just digital which isn't the same thing.
Upscaling is one of the more overused terms in the industry right now.
All upscaling does is ensure that the picture will fit your screen. DVD is somewhere around 420 lines of resolution an HDTV is 1080 so do the math. The picture would barely fill half the space on your TV.
"Upscaling" simply has the the player "guess" the color of the pixel between two known pixels in order to make the picture fit the screen. Upscaling cannot add detail becuase the information for the extra detail (read: resolution) isn't there.