The summoners are kind of tricky. You really need them but having them at level 8 is kind of overkill at the moment. The gap in price between getting a level 5 having to buy single cards leveling them up and getting a level 8 which has 5x more cards into is not all that big though.

I have mostly focussed on buying cards that are most useful to lease out to affiliates, which has been a really good use case so far allowing to earn some good returns on those while I'll be able to sell them one day.