Is it worth getting a mid -roof?

I wouldn't bother if I were you. It's not worth it unless you wanna get rid of that truck for any other reasons. Yes, a mid roof it's more suited for tankers but I doubt that you will really see a difference in fuel economy running your high roof.
Are you thinking trading yours for a new one? The price of a new one just went through the roof due to the weaker Canadian dollar.
Just put in balance the cost of financing a new one or even a used one, cost that you will see on the paper with your loss in fuel economy running your high roof, cost that you can only guess.
Last time I heard there were 30 some factors which influences fuel economy. Speed and weight are among the most important ones but not the shape of the truck

Good luck to you

 

In the old days I'd say sure but with modern emisson trucks if yours ain't broke don't fix it .. The 2 to 3/10 ths you may pick up could be spent 10 times over on a troublesome emisson system .. If your current one is a good one Id run it till it dies ..

 

I'd say check with the company you're going to. When I hauled food grade there were quite a few customers that were 12' or less and a high rise obviously wouldn't cut it.