You can check out our guide to Magic: The Gathering Booster Pack types here, but the short version is that Collector Boosters are filled with alt art, foil treated and special variants of cards in any given set
When combined with other cards that trigger multiple instances of life gain you can watch your creatures get stronger and stronger
If these cards are to be printed, then that's great, but just put them in the decks and maybe make a couple more per set if needed
Then your critters also gain affinity for +1/+1 counters, so that'll be super easy to cast as well
Many collectors consider this the most iconic EX-era Pikachu ever printed, and the price reflects it
Additionally, you will find it important to balance the power of your deck with the consistency and overall synergy