IMO:
I think the lack of X notes, the rather uneventful $10 Birds. has made collecting the 2001 Journey $10 a very challenging/intriguing ambition. Its contrary to what anyone would have expected in the way it was released and withdrawn.
If you can lay your hands on a $10 BEL, BEK (esp non-insert), or a 2003 BER (in any shape) than you've got a fairly scarce note -the envy/prize of a growing body of collectors.
You can also get a 2003 BEP, insert BEK, 2004 BET/BER, 2000 FDY, 2001 FEE, the ones I mentioned earlier (FDZ Knight/Thiessen $10 or the new 2004 FEV $10) and you've got some rather rare key notes. These notes are essential to a complete a collection of the new notes and yet (with the exception of the FDZ/FEV) they're not inserts. There is speculation that the 2003 BER could have been reserved to act as inserts and the 2004 BER inserts naturally command a premium. Fewer Knight/Thiessen notes printed on documented flimsy paper, the missing circle anomaly, and the counterfeiting notoriety/scandals endow this series with enough variations, short prefixes, and bad press, to make it fascinating/compelling to complete. The Journey $10 notes (although the butt of many jokes for their colour/lack of compelling security features) ended up becoming the "sleeper" series.
Most collectors know the significance of the notes I've mentioned here and yet most aren't inserts. I know this may sound crazy but I think that this recent phenomenon of special non-insert releases of 2001 Journey $10 has been a needed shot in the arm for note collecting. I think it may have brought more collectors into the community. Most of the collectors/dealers who actively fished these beauties out of bricks knew (in a latent way) how rare they were. I know that many brick searchers regretted selling them for what they did!
I believe a lot of collectors had hoped the Journey $5.00 would follow suite (in intriguing notes to collect) but they've been disappointingly conventional and predictable. The only notes that seemed to generate any excitement/interest were the AOF / 2004 HOH but these pale compared to the $10. I'm not talking about inserts here. I know the hard-core insert collectors are probably screaming about the HOG inserts and I'm sure there's many good notes I'm missing. Perhaps the upgraded notes have more surprises in store...