In the burning crusade there will be
13 new 5 man instances ranging in level from 58 to 70
1 new 10 man instance - Level 70
5 new 25 man instances - Level 70
---- Compare that to non-expansion wow ----
19 5 man instances (combined wings)
1 10 man instance
5 40 man instances
2 20 man instances
The first 2 5 mans, Hellfire Ramparts and the Blood Furnace give ZG level green\blue drops. The Ramparts are 58-64 and the Blood Furnace is 59-65. So right off the bat, while not immediatly upgrading T1 items, people without T1 or ZG or AQ20 stuff, will be able to get gear fast. And people with T1\T2\AQ20\ZG gear will still find these instances fun and easier to do then those with straight blues\greens.
--Oh yeah, and there is a lot of faction grinding in the expansion, alot, sorry to inform you.