Mainly for the foliage although they produce a great tasting fruit from what I have heard... white variegated bananas (as you know) are rare while red variegates are fairly common (i.e. rojo). While there are other white variegated bananas (freak orinocos and basjoos and such) they tend to be very weak and a darn pain in the back to keep alive and looking good. The Ae Ae on the other hand tends to be a bit more robust... it is still finicky from what I understand but a whole lot less trouble than others.
The price is also driven up by the fact that they are only reproduced from pups... TC has been unable to successfully clone a variegated Ae Ae and they don't produce seed.
I am sure other members here who actually own one could be a bit more help I am just basing my info off of first hand accounts of others growing experiences and banana information resources off of the net.
However I would be just fine and dandy with an all green Ae Ae just to try to get it to fruit
Regards,
James