"Truthfully I dont think that rarity matters for the value of cards"
It is one part of the pricetag, its simply matter of supply that makes even sub-par rares have OK pricetag. Price of card is made up on roughly (but not limited to) these things (not in order of importance):
1) New Blood status (or recent newblood status) (newblood supply status)
2) How popular clan is on pack
clan picks (supply status)
3) Price history (expected price)
4) Absolute play value
5) Position to next best alternative in-clan
6) Relative price to alternatives in clan
Is card part of possibly CR-getting clan?
9) Recent takeover attempts
10) LD related price changes/expectations
11) Market play around that card
12) How much investors needs money overall currently. (aka. Keep or sell decisions)
13) Metagame changes
15) Card level
16) Card suitability for pfull scene
These are some of the factors that make cards have certain pricetag each moment. These things affect both the short time and long time prices.