I believe Mid School prices will equal and possibly surpass those of Old school (broadly speaking) for a few reasons.
1) Any collecting / hobby prices peak when the generation who aspired to it back in the day as their greatest disposable income. So for example, if you were 10 years old in 1984 and drooled all over the Hutch Pro Racer in your local store but couldn't afford one, chances are when you turn 40 you will have more money (and a mid life crisis) and pay top dollar to now own the bike you longed for as a kid. This pattern drives the prices up and acuses the "peaks" in value you see every era go through 20-30 years after it originally happened. Just like old school, mid school will also go through this in 10-20 years time.
2) Bikes were made in far fewer numbers then old school bikes. By the very nature of the fact there are fewer mid school bikes around when the peak hits one can only assume people will pay more to get their hands on one. You can already see this in the prices of 1st Gen Hoffmans, Haro Airmasters, Early S&M, WAL, etc, etc are already fetching prices that rival some of the most desirable old school bikes. And keep in mind the Mid School bubble is still growing as the 90s generation of riders comes around.
3) Mid School was just way cooler in any case.
Saying that, at the end of the day does it really matter? I certainly wouldn't advise anyone to consider hoarding bikes as an investment. If you do that you will live poor, and die poorer.
