Initially, I planned to developed ALL CL cards I was interested in up to a certain level by buying what was needed from the market and then hold, waiting to get the rest by opening the packs. But I think I might change the strategy. And will probably max some cards (summoners included), and maybe not open a good chunk of my packs at all.
I believe that it doesn't make too much sense to develop all the cards. There are some cards that I have never played so far and I don't believe that they will be necessary for my gameplay. I start to develop summoners and then some selected cards that I need.
You will never know. These past few days I used one card I haven't developed at all and probably never will. And yet, it proved useful in a certain context. Strategies evolve, I've made the mistake of discarding many cards as not useful or not to be upgraded above a certain level in the past. That is until I met it in combat and that particular card I thought I shouldn't upgrade made the difference. The opponent had an extra ability or a higher attack power or higher life or speed, and that's how the battle history was written.