Yes! Two tiers is enough. Many brides report having a lot of leftover cake with the two-tier Escape wedding cake. Disney may tell you that a 2-tier cake only feeds 35 or some such nonsense, but we had 35 people and there was a LOT leftover of the two tiers we served. Now if you want to save the top for your anniversary, there won't be enough. But if you eat the whole cake, you should be fine.
Also, usually the mad hatter cake is done as three layers, so they may be resistant to changing it to only two...
When I talked to Rosie from Disney Floral, she told me that we are allowed to take our cake with us (we are having an Escape wedding.) She said they will box it up and we can do whatever we want with it.
Some Wishes wedding couples have been told they can't take theirs home (besides the top layer), but then all the leftover cake turns up in the box with the top layer, so...
We were an Escape wedding and we got all of ours. More than we could polish off while we were there ! Boxed up and put in the trunk of the limo for us with all our other stuff while we finished pictures !
DF is worried the cakes look small and there wont' be enough for all 19 of us. I keep telling him "the girls on the boards say it's plenty" but for some reason he doesn't trust in the vast knowledge that is the disboards!!
I've asked my planner for the cake dimensions to ease his mind. He manages a grocery store and he keeps telling me the portions they use to tell you how many people a sheet cake will feed are tiny, and he wants our guests to get full pieces of cake It's funny the things he's worried about would never cross my mind. But I'm glad he cares!
I bake wedding cakes and I can tell you that they cut large pieces and we had plenty !!!! They are not the typical serving sizes the wedding cake books talk about. Each layer of cake is around 6" tall for starters, and I think about 4" deep and 3" wide. Plenty to eat !!! I don't think anyone even asked for seconds and most weren't even able to finish their pieces.
We had a ~60 people and had a 3 tiered cake. The two bottom layers feed our guests with cake to spare. But I don't know what happened to the leftovers. However, we did get our top layer and it was lot of cake. I attended a DL wedding that had the 3 tier Mad Hatter cake and it was more than enough cake for a group of 75. I know that we were told that it would easily feed 75+ when we considered getting it. HTH.