I would comment that the only problem with getting the members who are ready to raid Kara going is that they will get burned out on Kara very quickly. So that when the last of your members are starting Kara the others will not want to go and you might come accross the problem of motivating the players that have all of their gear from the instance not going. So in that situation I can appreciate the holding off on Kara though I know the exact position you are in right now.

Also what about the people who are going slowly? Do they even want to raid? Will they really get jealous of missing the fun? Just a couple of things to think about in general not to really knock on the situation. Good luck with your guild's future. Perhaps like people said find out what your guild wants (the members who are not leveling very quickly) and then find out what you need to do to get your guild raiding. If some of the 60's are interested in raiding and they are leveling slowly maybe try and motivate them to level faster if that is really their goal. Then when you find out what you are short on maybe open up the doors for a small recruiting drive? I don't know. I am bored on vacation throwing out some ideas lol. Anyways good luck to anyone stuck in this position.