I actually got into laserdisc after dvd came out since it was so cheap then. Once I saw that Escape From New York and Halloween had special features the dvds didn't, it was off to ebay.
For what I saved buying Criterion's The Killer and This is Spinal Tap on laser insted of the dvds, I'd say it was all worth it. While most of my collection has been issued on dvd, there's still some gems (extras-wise) that are dvd only.
My favorites:
Menace II Society (only uncut version on any format, 2 commentaries, music videos)
Leatherface TCM3 (2 commentaries, both far better than the cut and paste job on the dvd, and no annoying studio exec. taking it all up with his anedotes)
Sid and Nancy (stuff about teh real band not on the dvd)
The Demolitionist (commentary and widescreen)
Nightmare on Elm Street SE (amazing that all these deleted scenes still haven't made it to dvd)
Halloween Criterion (the Siskel and Ebert review is almost all that's left, but is worth the price)
Escape From New York (now just for the foldout of greatr artwork)
The Howling (for the full deleted "hot tub scene" which got partially put on the dvd, and the interview with the stop motion effects guy who's work got cut, plus the nice big art)
Dead Presidents Criterion (commentary, esp. with Keith David, who just has a voice I love)
The Killer and Spinal Tap, for saving me hundreds of dollars. Got both of these and a player for less than an average copy of The Killer on ebay.