Look, I know I criticize a lot of your posts, and I'm not saying that you don't have a point here, but can we just think about this for a minute?
First, on behalf of your argument, yes, college (and pro) sports attendance is on the decline.
But on the other side of this, the "half-filled" argument is currently true largely because of how bad the team has been for 15 years. And it also overlooks our "big" games, such as F$U/VaTech annually, or Florida/Notre Dame occasionally.
So think about it this way. Let's say we build a 30K stadium based on current trends. What happens when we are good again, and 60K want to come to the games (and don't tell me about how they should have been fans all along, and they should pay a higher price, etc.). I know that the fans don't come out in droves when we suck, but if you cap our attendance at 30K forever, it will be nearly impossible to ever build a loyal fanbase in the future, since it will be a small and rare group who gets to see UM in person.
Additionally, you would lose the chance to ever schedule some of those top teams, since the Gators and Irish (with huge fanbases) are never going to schedule an away game in a 30K stadium (similar to the way they won't play UCF in Orlando). And don't tell me about having the "big games" in Hard Rock. They are busy turning that venue into a multi-use tennis/Formula One facility. The LAST THING that they will want to do is to drop everything just to host one or two UM games every time WE NEED THEM (and they don't need us).
There is a part of your argument that is appealing, in that I chose to go to UM because it was much smaller than UF and F$U, but from a sports standpoint, we will really put ourselves into a G5/service academy box by playing in such a tiny venue.
Miami needs to work on building the fan-base, building the attendance, and making sure that we CAN fill a 65K stadium every single time.
And, yes, winning helps.