Let me preface with I don't think you made a mistake to book a 1a cabin on a Millie class ship... I think they are just fine, and were before the change t... and this is my theory on the whole thing...
The 1a has always cost a bit more money than the 1b, and it looks like to me the differential is pretty close to the same as it use to be... so your not paying much if any more for a 1a now than you were a 1a before the "change".
All of the 1a cabins on Millie class ships are on the Sky deck, and all but the four on the stern are affected by the "overhang". That is, the Resort deck above extends out from the sides of the ship so that the 1a balconies on the sides of the ship are completely covered from above, and the "overhang" even extends several feet beyond the balconies, too. In addition, some people are concerned about the potential of noise from the resort deck above (and there have been some complaints of "chair dragging sounds", etc.) So, a lot of people have complained about the "overhang" and or "noise" and as the word got around, it was becoming increasingly difficult to get people to book them (except for the ones on the stern, of course... those are VERY popular, and there's usually a waiting list). So, Celebrity introduced the Concierge Class to make them more desirable and I'm sure are hoping as a result, they'll get more people to book them and not avoid them.
Personally, I've stayed on the Sky deck (in a cat. 3 admittedly, and not a 1a) and didn't find the "noise" to be a problem. I could see the "overhang" from my veranda at the corner of the stern, and it didn't look like a problem to me, although I can see how it might be for a "sun worshiper" because there won't be as much sun. Personally, I'd rather have the protection the overhang gives from the elements.
So, I'd say the Concierge Class is a good deal, since they really don't seem to be charging much if anything more for it, and the cabin would be a good one. But again, personally, I won't book a balcony cabin unless it has an oversized balcony, and you can only get that on the stern (those cat. 1 balconies are huge).
So, I hope this helps. There's some good pictures of the "overhang" in the photo gallery archieves if you want to see.
paul