There is no killer quality increase from DVD to Blu-Ray the way there was from VHS to DVD.
I have the sneakiest suspicion that a lot of people that adopted the DVD format were in it for more than just quality. Sure, it was a nice bonus - but VHS (and VCR's), by design, were always a pain in the ass. You had to rewind the tapes, you couldn't jump around, they had this nasty habit of breaking, you had to fiddle with the tracking, etc. It didn't hurt that DVD players and the discs themselves were eventually priced to move (unlike Laserdiscs).
I'm going out a limb saying that if the only improvement between VHS and DVD was quality, we'd still be renting tapes instead of discs.
On the flip side, Blu-Ray players are coming down in price enough where anyone in the market for a new player might spend a little extra coin to get the higher quality. I'm on the fence here - so I'm just sitting back with a wait and see attitude.