Right now I think it wouldn't make much sense to implement a lot of low lvl dungeons, cause majority of the playerbase is up in the 50s. But for 2.0 they better have a hand full of in between dungeons ready, or the same cycle will repeat itself.

I'd say at least 2 dungeons for each 5-10 Lvl ranges. So like this...

Lvl 5-10: 2 Dungeons
Lvl 15-20: 2 Dungeons
Lvl 25-30: 2 Dungeons
Lvl 35-40: 3 Dungeons(since you spend more time on those lvls)
Lvl 45-50: 4 Dungeons(to get gear for the endgame stuff)
Lvl 50 Endgame: 5 Dungeons + some free roaming NMs(to maximize your gear)

And that's what I "demand" for 2.0 at RELEASE...obviously there should be more down the line!