The math is a little off because the average price is $75. And the price of tickets tends to go up with inflation and cost of living. But you are generally correct - the longer you keep your season tickets, the lower the cost of the initial investment. This is one of the good things with PSLs - they encourage long ownership.
PSL seats are very, very rarely vacated. Jacksonville is the only city I know of where this has happened on a significant basis, and that is because the value of PSLs has plummeted.
In every other area, PSLs are very active on the reseller market. This becomes the preferred method of upgrading or changing seats. In fact, most teams have sites set up for the sole purpose of reselling PSLs, after all, it is in the team's best interest to keep the PSLs sold as well. Now as with any reseller market, whether or not you get face value for the PSLs has a lot to do with the location of the seats. Just like with regular tickets on the market.
Truthfully, you probably won't get face value back for the PSL unless you are on an aisle or have prime seats. But you will always get SOMETHING. Vacating the seats just doesn't happen.
Check out
https://rams.seasonticketrights.com/...rketplace.aspx to get a good idea of how the reseller market works.
This is a fact, and is a side effect of PSLs. The number of season tickets WILL go down initially. And it will take several years to build back up. But as it does, the season ticket market will actually become more stable than it is now. And there will always be tickets available for people who would rather buy from resellers or single game tickets. That is part of the game...