Hey mate, really suggest buying the cards that are really cheap CP/$. You can also use the cards to win more, or rent them if you don't want them later or sell them (hopefully at a profit).
Currently if you just bought the lowest cost per collection power it would only take $48 USD to get the 15,000 CP needed for Silver 3 where the rewards are much better. This difference in rewards will be widened in the new rewards revamp too.
Use https://peakmonsters.com/market and go to the compare tab and sort by best CP/Cost ratio to find these stats.
Spending 450 DEC currently about $0.71 USD at the end of each season is $18.46 dollars per year just wasted and you don't get to enjoy the game as much without cards to play with. Plus you will get better daily rewards in silver 3, which is and extra $0.10 USD per day compared to bronze 2 which will pay for more than the rest of the cost. You also will get air drops of SPS because of the cards you own. All of these factors make the choice very simple in my eyes. Along with getting more enjoyment of the game in silver 3 instead of fighting the boring bot armies in bronze.
You can check the average rewards of each league here.
https://www.splintercards.com/tool-lootchest.html?tier=4
Just a my perspective that I think could be helpful.
Cheers for your great content
!PIZZA