Yah, I took that into consideration. Based upon my routes and what I've read is a fairly good chance of succeeding, I am assuming that 75% of my and the wife's seats will be successfully upgraded and the other 25% will fail. If we wind up with 50%, still worth it. 25%, probably not.
To the OP: you do realize that PLT domestic upgrades are not automatic at 72 hours, but rather will be considered starting at 72 hours? You'll still be behind all the EXPs. As a PLT, my upgrade % was pretty high. However, depending on the routes (and esp. if you are trying to upgrade two people), you may well still find yourself in coach.