I find myself ALWAYS watching the disk of extras over a movie, no matter how much I love the movie. I put the Incredibles DVD in my player once (to watch with commentary), but never stopped putting in the hefty bonus disk for the behind the scenes footage, the film universe stuff, the Bud Luckey retrospective and short,and especially the Clutch Cargo parody.Extras and behind the scenes stuff are nice, but I don't need a whole other disc of them, and with my time these days, I'm lucky I have time to watch films let alone extra features so it's not a priority for me anymore.
I don't think huge DVD bonus features make the set, but there's always stuff that NEEDS to be bundled with a movie... extra scenes (be they deleted or alternate) if available, and some sort of cast and crew commentary and or interview. Deleted scenes show you what a movie could have been.
I hate the slim disks with nothing. Shows a lack of care. Things aren't always available, sure... deleted scenes in a lot of older movies went right into the trash... but at least find the least famous person in the movie and interview them.