I have pretty mixed feelings about all that. It's rather clear that demand has always played a huge part when it comes to trading and I don't think it could ever be avoided. But... I feel like the situation was completely different few years back. Now it seems like except pets with huge demand, such as old Store pets which are never re-released, most of ex-lists aren't very much appreciated. Of course people get happy if they get them, f.ex. on 18th December, but trading them off for something with bigger demand, even if one's overpaying... that's way trickier.
I am fully aware that now, with discontinued rares list, there isn't really a rarity guide, but that makes it even worse in a way... Many people still have the list somewhere back in their mind, it's not like there has been such a big change in the value of pets, but it makes it very confusing to figure out what's a right trade and what's not. Demand for certain pets just keeps getting bigger and bigger and other ones seem to be almost forgotten. Without having pets with high demand it makes it extremely difficult to trade for any pet with higher value. People don't just want ex-lists anymore, almost everyone wants the same pets and it has taken a lot of fun out of trading. Most of them will never be re-released, more and more players are joining CS, so of course the demand keeps rising... And trading for high value pets gets more and more difficult. I've had plenty of different (ex)list pets since I have joined CS and back in the time it was pretty easy to trade for other ones, because the demand wasn't THAT important.
I read all posts in this topic and I completely adore the idea of making a re-release box in the store. I heard that Store pets aren't getting re-released because it would be unfair to people who have purchased C$ in order to get them. If getting the re-release box would require C$ (and would be also limited the way that 18th December adoptions are, maybe 2 or 3 pets per person), then it could be a huge game changer. It wouldn't be unfair to people who have purchased their Store pets and it could really improve trading possibilities, also for new players. Of course not everyone has to have all valuable pets, but I think it's ncie if everyone has a chance of obtaining their dream ones and, to be honest, at this moment lots of old Store pets are completely out of reach for new players/the ones that don't have lots of valuable pets with great demand.
EDIT: I just saw that it was mentioned by Tess that store pets are never going to be re-released no matter what, so I nevermind it I guess ^^' I understand the reasons behind it, but I just wish people were a bit more focused on other pets too