Two points:
- Rarity and value are only loosely correlated.
- You can't make people want certain notes. Even with the power of sellers to set the prices they want, they can't make people pay those prices if buyers are not interested.
Popularity is a stronger variable at determining value. That's why you can't compare two different notes of equal rarity and say that because one is worth such-and-such amount, then the other one must be worth about the same. If one is popular and the other is not, then chances are the popular one will be worth more.
On the second point, it's no secret that efforts to keep the prices high for certain notes have backfired. I am thinking specifically of the Lawson-Bouey X notes. For a long time, they have catalogued much more than subsequent X notes, and I am guessing that this is due to a long-standing perception that they are scarcer because fewer were saved before their identity as replacements was recognized. However, it appears enough of them were saved to supply the soft market, and people who speculated on them keeping their value or going even higher are feeling burned. It takes a long time for people who paid too much for a certain overpriced note to accept that their investment was a bad one. They will keep asking the same high price for a long time, then give up if they can't find a sucker.
On the question of whether Journey series inserts are scarcer... Well, some are, and some are not. Again, it's not scarcity that determines value. Certain prefixes and ranges have gained popularity. Many have not. I think that insert notes as a whole suffer from the "so what" factor, meaning collectors look at them and don't feel a need to have them. Part of that is probably the simple and obvious fact that inserts look like regular notes and were printed like regular notes. Only after they were printed, they were set aside from the rest of the regular notes and used to replace defective notes. That really amounts to nothing in the grand scheme of things because all the notes are put into circulation, and the only difference is a few notes from a few select ranges were put out to circulation in a different order from the norm. I doubt that anyone is trying to collect one note from every ream issued. Some people try to collect one note of every prefix, and when you tell a prefix collector that a run of 1000 notes in prefix AOP was used as SNRs (7.075-7.076), that person is probably not going to say, "Wow! I simply must have a note from THAT particular range!" Instead, they will probably say "Well, I can achieve my purpose by buying almost any other AOP note." The point is, AOP notes as a whole are not scarce. There were 10 million of them printed, and 9.999 million of them catalogue $6 in Unc while one run of a thousand notes catalogue $400 apiece. You can put one regular AOP note next to a replacement AOP note, and unless you have a catalogue or insert note list in hand, there is nothing to distinguish the two notes.
Nobody wants to be a sucker, and everyone wants to get into a good investment on the ground floor. Maybe a lot of collectors look at insert notes and think there is no ground floor. From the minute an insert range is confirmed, notes from that range sell at a price set by whoever finds these notes.
Trust is also a factor. The big question insert collectors have to ask themselves is, "Are all notes from an insert range issued like true replacement notes?" From time to time, huge runs of insert notes are found like regular notes, prompting us to believe that the answer is no. Even without such compelling evidence, simple logic tells us that if a bunch of notes set aside for use as inserts is not used up because there were not enough defective notes needing replacement, then those remaining notes are then issued like regular notes. And why would they not be? They were not part of a separate printing order; they were part of a regular note order and were simply put aside for another purpose. To complete an order of a certain number of notes, the printers have to make a few more notes to make up for the defective sheets/singles removed, and this appears to be why a lot of series end in smaller reams than expected. I would propose that it is those end-of-the-series reams that are the true replacements because there is a strong probability that they were not printed at the same time as the rest of the notes that preceded them. Insert notes simply make up for missing sheets/singles; they are not actually replacing anything in the entire order.
Think about it like you are the Canadian Bank Note Company. You get an order from the Bank of Canada for 100 million notes. This will take a few weeks, and your well-paid quality control staff (QCS) are not sitting around smoking cigarettes while waiting for you to finish the order. They are pulling out defective sheets at a rate of 0.4%. You are too busy filling the order to print up replacements, so your QCS use notes from the same order to fill up bundles and bricks. They keep tabs on the number of defective notes removed, which in this case is 400,000. You can't ship 99.6 million notes to the Bank of Canada and expect them to think you sent them all 100 million notes. Hey, you are in the business of printing money, but you can't just print your own profits! So you make another order of 400,000 notes. No problem, that's one ream of 360,000 notes (45 notes per sheet multiplied by 8,000 sheets) and one ream of 40,000 notes (45 x 1,000 sheets). If there are any defective sheets in that smaller order, you use the extra 5,000 notes you printed in that small end ream. If you have leftover notes, those go in the furnace as it's doubtful the Bank of Canada is going to let you hang onto notes that are unaccounted for. So in the end, you printed 100.4 million notes to fill an order of 100 million. Those 400,000 notes your QCS used as inserts could have come from anywhere in the order.
Compare this to the old days when replacement notes were printed separately. Those notes were the actual replacements in the order, meaning you did not have to print up more later to make up for defective notes. Unfortunately, this means you always have to keep a surplus of them to avoid running out. And if you really mess up a lot, you're going to run out. On the other hand, if you do a really good job, you end up with a lot of extra replacements that can't be used, meaning you wasted a lot of paper for nothing. You're screwed either way! The modern insert method makes a whole lot more sense because you only ever print up as many extra notes as you need afterwards, so there is no guess work and no having to switch back and forth from printing regular notes to replacement notes and back to regular notes, etc.