I've always been opposed to changing the advanced class. There's only a few choices we make that actually matter. This is one of them.
Besides, if you reroll then you can always choose the different path (light or dark) than you did the last time to see the differences.
I've always opposed the idea too but its sort of growing on me now. I honestly wish that at lvl 10 that you could play each AC for a certain amount of time before making your choice, that way you've got a taste of what each class is like and you can choose the AC that fits you best. Then we wouldn't have to worry about AC respecs in the future.
However, I don't think you should be changing your AC later on just because your spec you run got nerfed or the class got nerfed in general. What if juggs/guardians got nerfed and many of them wanted to switch over to a mara/sent because once again they got another buff? We'd start seeing a class unbalance and that's not something you want. If they do introduce AC respecs in the future, in my opinion it should be a one time choice, no second chances. Once you've changed, you've changed. Done.