Chaos Legion rewards have been out for almost two weeks now. The general consensus is that CL card prices will trend lower as volume increases. This is not awful for the game though, because new players need competitive cards to collect that are accessible. If you have just started playing, try to make builds around the new Chaos Legion cards.
On the otherside, people that may want to speculate on future card prices will have to stick to out of print cards. My only thought would be aiming for trading cards that will gain a boost in utility when paired with a CL card. The out of print card would have increased demand and use without a changing supply. The Chaos Legion edition will eventually be the most prevalent card on the playing field so finding a benefiting card will be fruitful.
The risk is also there because some cards will have value greatly diminished as a CL card provides better playing opportunities. One quick example I can think of is how Sandworm used to be traded at 3$ per level 1, and now it is about 1$. The main reason for Sandworm's price cut is due to the neutral armoured snake Uraeus.
Aside from card prices there are chances of pulling great rewards. The second end of season CL rewards are upcoming with plenty of profitable cards to be earned. Keep grinding daily quests because you may be lucky with a gold foil.