Personally, I think it's a great idea, but, like you said, it's a lot of work for 3 more inches.
Are we talking streach the frame too or cut into the bed?
The problem with cutting into the bed to me is a big problem. I like having an 8 foot bed. That's why I would never buy a dodge mega cab. (except for the one below)
If you streach the frame, we're talking adding length to the driveshaft, brake lines, fuel lines and the electrical that goes to the back. I'd say to add another set of doors if you're going to go through all that trouble. Hell, I dream about having another two doors on my crew cab. I might do it too one day when it isn't my daily driver. It's hard enough to park this thing in the small spaces at the mall when it's crouded the way it is. With another two feet, hard enough just moved up to impossible.