[theseeker]

why are mid-grade sets from the seventies not considered an investment? The way I see it, it's supply and demand, so if interest drops in these sets, it will be across the board. As a matter of fact, high-grade investors are likely to take the bigger hit. It seems to me, if history is any indicator, there will be proportional price movement, according to grade. All the price guides have a means of pricing sets in various grades. High-grade sets sell for more but, obviously cost more and are more time consumming to obtain. And one more thing to consider, they are less liquid as they tend to take longer to sell.
It's all relative, if you're trying to complete a mid-grade set, then you complete it with mid-grade cards. For bargain hunters, there is greater price fluxuations with mid-grades, so it could be worth the effort to complete the sets. Of course, as the saying goes "time is money."
P.S., why are seventies sets now "coming out of the woodwork?"