The ilvls don't match up directly on gear. An ilvl x green is vastly inferior to an ilvl x purple. You can really only use ilvls as a comparison within the same quality, ie. comparing green to green or purple to purple.

For a more concrete example, I've got a Breastplate of the Lightbinder, an ilvl 115 purple healadin chest piece. http://wotlk.wowhead.com/?item=28662 The first blue upgrade to it (at least that which is listed in wowhead) is Chestplate of Northern Lights, an ilvl 155 blue item, which requires a minimum of level 70; probably, that's going to drop in a 72-73 instance or come from a level 72-73 group quest. The first green upgrade in the database, in case I never run the instance or the item doesn't drop, is Norrington's Burnished Breastplate, an ilvl 162 item (with no int, so it's hard to say that it's even an exact upgrade, and it may be slightly inferior), which comes from a level 77 quest.

Mind you, the purple 115 ilvl item is a drop from a (relatively) easy boss in Kara; if I saved up the 100 badges (which, in the grand scheme of things, isn't that much if you're already running kara), I can grab the Ecclesiastical Cuirass http://wotlk.wowhead.com/?item=34921, which will may take me into Naxx, or at least up into the 78-79 dungeons.

To sum up, grabbing gear now is still worthwhile. Run Kara and buy badge items for now, if nothing else. If you can't do that, then focus on getting alts leveled; that seems to be about the place where the divide happens.