I used this combo on my S Hollow, along with a maple neck w/ rosewood board.

There are a lot of variables at work, but I do think the quote above describes it well. Is anyone going know the difference when they hear it, other than me? Doubtful, but I like it and it makes me happy.

From talking with Tommy, you need at least a 1/4" top to really affect tone. A lot of the ash was actually cut out of mine (arm contour, f hole, universal pickup rout, control cavity, trem), but I still perceive a difference.

I guess you need to consider why you don't want a straight ash or alder body. If alder isn't bright enough, but ash is too bright, the ash over alder combo could be a cool idea.

I bet it would look great with a sunburst finish - ash on the front, alder on the back. Amaze your friends! :p
--Garrett--
G-tars