You're still not getting it, Jay. Suddenly having a MitB winner lose when he cashes it in isn't going to really change the world.
The fact that we know, with almost 100% certainty, that the MitB briefcase holder is going to win the title when he uses it is part of the appeal. Aside from RVD giving Cena advance warning, every use of the case has been a surprise and, more importantly, a successfully executed angle.
There was excitement with every single one of them, the fans reacted accordingly (booing Edge both times, cheering Punk on his first one and then booing him to high hell on the second) and a memorable moment was created.
I mean, let's just take the last one as an example. We all knew Punk was winning when he cashed it in, but we didn't know when that would be. The entire "WWE Universe" were almost rioting to get Jeff the championship and, at last, finally, he had vanquished Edge and reclaimed the belt after a brutal TLC match. The fans are on cloud nine, Jeff is the champion and has the look of "it was all worth it" on his face, JR's about to interview him... and then Punk's music hit. The fans go absolutely mental, I personally go apeshit at what's about to happen (especially as it was how I said Punk should cash it in) and Punk begins his turn into what we see today.
Not a single thing about that entire situation was stale. Knowing that Jeff was going to lose the title he had just spent over 20mins winning back was part of the appeal and the reason Punk was booed so loudly. If you can't see why the concept simply works, then there's not really anything else that can be said to convince you.