As someone new to the hobby I've found it difficult to decide when to buy new games. There are so many recommendations and "essential" games it can be very easy to quickly overbuy. Many people use monthly board game budgets but that results in the urge that you need to buy new games each month rather than actually limiting.

Personally I've tried to use satisfaction in my games to decide when it's ok to buy new games where I wait until I've got satisfaction equal to the game's value on over 75% of my games. This is probably around 15 to 20 plays of a £40-50 game where plays can take an hour or two. Though I have a different slightly different approach to print and play games due to the low costs, but I still try to play my previous printed games a few times before printing new games to experience as much as possible.

Living card games can complicate things as Arkham Horror The Card Game has expensive expansions with each one adding a replayable 10 to 15 hour campaign depending on the number of players. You will want to buy each campaign and hero expansion to keep exploring the theme and world but you will only get good value if you replay the campaigns. Because of this I plan to rotate my Arkham Horror campaigns so that I do get additional campaigns but replay older ones in the order I first played them in. Marvel Champions on the other hand has much cheaper expansions and a cheap £5-10 hero pack can add hours upon hours of content due to how you can configure all the game's modules.

Based upon my current experience I think having a board game purchase limit per month is ok as long as you avoid using that as a requirement to keep buying. Along with only buying games you know you will like without being too swayed by other's recommendations.