Hi Fourtyfour, I've posted your thread before, still subscribed and enjoying every one of your posts.
Looking at this picture and knowing your floor issues had me thinking of another thread on GJ.
Why not, put down a raised wood floor? You could install it to deal with the 1" down on that side, good in the middle and 3" down on the other side. As others have said apparently the NH winter can make a cement floor hell, well that would no longer be as major a concern.
Linked below is one of my other favorite threads as the OP, Wbrian63, is so good at detailing his work and is also quite detail oriented, but in the wood world. He is running a wood shop and wanted the ability for under floor dust collection as well as some of the natural flex for comfort that the raised wood floor offers.
http://www.garagejournal.com/forum/showthread.php?t=60859
I'm not sure if it is even a good idea for what your work entails, but you seem to be as good at building with wood as you are with metals, so I just thought maybe it could solve multiple issues with your older building. Perhaps you could even lay down some interesting hardwood and just richen that already sweet workspace even more. I think with your eye it could be an amazing addition.