Players or sets that were once hot but now are not

[Flyers16]

- 90/91 & 91/92 Upper Deck. Loaded with great players and lots of RC's but overproduction killed their overall value.
- French version of anything in the early 90's. The novelty has worn off.
- Seventh Inning Sketch Canadian Junior league cards. At the time it was fun pulling pre-NHL Lindros, Brodeur, Falloon, Daigle, Osgood, May cards but a combination of overproduction and sets containly a lot of players who never made a significant contribution in the NHL (if at all) affected the set values

[Rob PBS]

Jonathan Cheechoo!
(Which suits my wallet just fine)

[Johnsson]

I think most sets cool down with time but it seems to me that value of the "one per box"-parallels, like UD Exclusives and Artist's Proof, is at it's lowest point right now. Judging by pwaldo's Top 10-threads, those cards were among the most attractive cards in the mid 90's, so it's sad to see that there really isn't any demand for them today.

Going by BV a
2010-11 Artist's Proof is valued 10x Base compared to 30x Base for the 1995-96 version
2008-09 UD Exclusives is valued 6x Base compared to 80x Base for the 1998-99 version

There is no major difference in base-value from 1995 to 2011). The sets are almost equally rare (the 96 AP has probably a higher print run, while the 99-Exclusives are likely harder to find, though they are both numbered out of /100).
But the demand back in the late 90's was 5-10 times higher.