The other reason I thought not to mount the spare underneath is that what if you need it when you ARE off-road and the spare is nicely obstucted by the object that just bust your tire? And I won't go back to a 'donut' size (stock) spare cause it's oh so nice to only change one tire in a case of a rear flat tire and not kill the diff (already had to do that). I have 32's and hopefully will be getting 33's in 5K miles.
I see where you are coming from as for being a waste of a truck. I'ld say the guys that hack up the bed to put in a bedcage or vertical rear shocks mounts would be more a waste of a truck, but then again if I wanted my truck to haul *** through the dessert, it's a small sacrifice to make. It's all what you use it for. Mine is mostly a daily driver, hauls cones and such for autocrosses once a month, car-fetcher, play offroad, etc.
Wik my spare where it is, it hasn't hampered me too much hauling stuff. IF I know I'm going to need all the space in the bed, it's just a padlock to remove, undo the spinner and the full bed is free (although I'm wikoot a spare for that time unless I stnad it up in a corner, done that). If I do make something more like RedRangers but a little less of a profile, then, yes, it will be a bit more work to remove it to use the entire bed, but it will still be removable (2 bolts, 2 pins)
Thanks for the opinions guys. Keep 'em coming.