Raw lots of 50s-60s cards in all grades have steadily been increasing over the past year.
Here is an example, this midgrade 1960 Topps lot of 340 cards with no major stars or high #s sold for almost $1.30/card. A year ago, a lot such as this the average price per card would have been 60-75 cents/card.
http://www.ebay.com/itm/1960-Topps-N...p2047675.l2557
IMO, fewer sellers are selling on ebay and the supply has lessened. However, the demand has remained somewhat constant causing the prices of lots such as this to nearly double over the past year.
Almost 10 years ago I finished a complete 72 Topps PSA graded set...avg grade was 8.20. I got down to needing a few cards to finish. One was the notoriously tough 708 card and I wanted an 8. I paid almost $200 for a centered 8 then..... now you bid and win one for around $40. Too bad I didn't wait. IMO, many of these higher priced, previously low pop commons have come down in price due "prospectors" rooting these cards out in their raw state from shows, shops, etc and sending them in for grading. It is as simple as the increase of supply driving down the price in a case like this.
Based on cases like these with the low pops, I think it is unfair to argue that the collecting base is shrinking (dramatically if you read some assessments in this thread), it is just not growing as quick as it once did. These examples of price fluctuations are based on the changes in SUPPLY vs. demand.