I very rarely play tournaments and never buy more than 1 set of anything. So far I have all the big expansions including Legends and am about halfway through the 3rd cycle of boosters. My total card collection for Warhammer is 1407. Since I provide most of the decks when playing with friends and at clubs, I have divided my cards into 24 decks of 4 for each faction. This gives 58/59 card decks and I have distributed the cards as evenly as possible between the decks. I also try to keep the number of each type of card as even as possible. The special neutrals are divided evenly was well. Each Order faction has 1 deck with Lizardmen and 1 with Wood Elves. The Destruction factions each have 1 Undead deck and 1 Skaven.
This ensures that each deck has an equal chance of winning, so games should be decided on best play. Which cards come out can, of course, make a difference. At this stage it looks like I have enough cards to play plenty of variety until the cards wear out. I may add a couple more boosters to reach the end of the current cycle - less than 3 cards per deck per booster - but feel I have virtually reached the end of Warhammer. I shall still continue to play, but don't think that more cards will improve the game. This also happened with 'Game of Thrones', 'Call of Cuthulu', 'Magic'. 'Stargate SG1' and many others. No doubt it will happen to 'Lord of the Rings' as well, but some way to go on that yet. Cheers!