If I had my way, all monsters would be race templates to be stretched over a handful of core roles, with a level template and a "theme" template attached.
Take the mind flayer template, apply it to the lurker role, plug in a level template so that it matches your players, and for giggles apply the "Deciple of Fire" Theme for an elemental power that connects it to the other denizens of the lava fields.
Of course, I do understand that ready-made monsters are more useful to beginner DM's, but it would be nice if I didn't have to reverse engineer all the monsters I want to change.