My code is at
http://jsfiddle.net/user1212/G86KE/4/
The problem is in gmail it leaves an extra white space between 2 tables inside the same cell.
I have tried
I know this is not what you might be looking for but,...
Loose the spacer (spacer.gif), in order to loose the big spaces in a responsive email images has to be embedded in one cell per row, than will display all images block-ed.
Hope it helps, this was the solution I used in my case.
One cell per row: