OK, the veneer thing won't give you any tonal caracteristics(sp) since the volume is not enough to make an impact on the guitars vibration (resonance).
And I'm going to take that one step further. Mind you, I don't have any scientific information here to back me up.
I would think that a veneer would do no more for tone than a thick coat of paint. Veneer is extreemely thin and, as Maiden said, you have just as much glue under that
For a drop top, there is much more material to contribute to the guitar body. I would expect the tonal difference to be in between the two different woods used for the body. For instance, a Mahogany guitar with a Maple cap is going to sound somewhere in between the two. It'll have the mellowness of Mahogany with a little brightness from the Maple. I would even think that the thickness of the bottom and top could be used to fine tune the characteristics of what each tone wood offers.