Gaming - Mann Co Store/TF2

So I am struck with a dilemma and need some opinions. I have recently started playing tf2 after it was released free to play. For those of you who do not know tf2 is "team fortress two" a game put out by valve that originally cost money but has been made free to play. You might say "Well how do they make money then?" The answer is quite simple hats and other items are available for purchase in the store for real money and these micro transactions fuel the addition of new content and upkeep.

So my problem is this: I feel like I should give some money back to the game as I have already played for over 10 hours for free. I would like to gain something at the same time and so have been looking at buying these keys they have to open crates for an item. The only thing is #1 a key costs $2.49, and #2 the item you get is not set, it is randomly chosen from a list and can in around 20% of cases give you the weapon you start with which in my opinion is a waste of money.

So I ask you bloggers, what should I do? Does anyone know if it is worth it to buy keys? Apparently after even one purchase your chances of finding items randomly, (what I have been doing up until now), increases. Does anyone know if it is a substantial increase? Post your opinions below!