The thing I don't like about teh 1 minute/level duration is that you preety much have to cast it in battle to get the use out of it. And since your wasting more than just a spell slot, your also using a standard action... that +4 to a stat starts looking preety lousy.
When I could casting scorching ray or invis in a combat, getting the +4 to a stat doesn't seem worth it.
A lot of people went with 10 min/lvl, because you could still cast them at the start of a dungeon and make good use of them, it wasn't the all day buff routine but it was still good.
Finally, the 1 minute/lvl makes extending them mostly pointless. 10 min/lvl extended you still get a fair bang for your buck.