I still have, oh, i don't know how many, functional DVD players around the house. 100% of my 'shiny discs that contain video' are playable in my current players. I'm unimpressed with HD. Sure, i can see the difference, i know it's there, but it doesn't entertain me any more than SD does, so i have no incentive to upgrade. I suspect i'm with the (possibly nonvocal) majority in this aspect.
Maybe when sufficient of my players have died that i need to shop for a new one, and the prices are sufficiently low on HD players, i'll consider it. But even still, everywhere i shop, BluRay copies are always at least $10 more than DVD copies. Who cares what the cost of the player is if i spend $10 more on every single movie i buy? It's just not worth it, and that diminishes my already nearly nonexistent incentive.
I guess if your TV is small, 36" and smaller, you really may not enjoy HD. Anything bigger and you definitely will enjoy HD, no matter what the content is.
I love to watch documentaries, nature, science, history and any of those are so much better in HD.
The largest TV I ever had is my current one which is 32". Even with it, I appreciate HD a whole lot more than SD.
I sit fairly close to the TV to be able to see the words. I cannot hear what is being said and I cannot see the words from a distance so I have to be close. Being close effectively makes the TV seem larger and I notice the imperfections of SD a whole lot more.