I started playing this game mid 2010. Liking to experiment, I had the plan to buy all third level runes, so I could make some weird builds. I don't play enough for this plan, so I considered buying the IP boosts, so I could buy more runes. Here's why I didn't do it.
There are two currencies inside LoL. One you can get by playing, the other you can get by paying. IP and RP, respectively.
There is a direct translation between RP and currency (dollar, euro, etc). There are a few things you can only buy with Riot Points (RP) and some things you can only buy with IP.
There are some things you can purchase with both RP and IP, hence a worth translation between them.
First of all, IP is gained per game. Quickly looking at my match history, in 10 games the average is 93IP per game. Being generous and round, it averages 100IP per game.
You can buy, at the best price, 9300IP for 50€. That means you get at best 186IP per euro.
Looking at the champion list, which you can buy either with RP or IP, you get an average of 4.6 RP per IP.
IP Boosts, double the amount of IP you get per game, so instead of an average 100IP, you would get 200IP per game.
Now that we have these values, let's look at the IP boosts. We'll only look at the best value ones.
The 50wins boost, costs 2560RP. This means that you would get an 50*100IP with this boost. So you are trading 5000IP for 2560RP, at the ratio of 2RP per IP. Which is less than half of what RP is worth, when buying champions. A bad deal. If you use IP gained this way to buy champions you are losing more than half its worth. You should really just use the RP to buy the champion and be done with it.
The 30days boost, costs 3490RP. The IP you can get with this is limited. Assuming a League of Legends game, averages 30minutes. 3490RP, at the ratio you can buy champions with, translates into 3490*4.6IP = 16054IP. So you have to win this much IP playing games, just to break even. At 100IP per game, this means 160games, and only then you would start to profit from this boost. During the 30day period, this means you have to play 6 games a day, just to get some benefit from this boost.
Remember, I was generous with these values, and went for the best ratios. Any other choice would worsen the conditions.
So what to do?
- Buy champions with RP not IP, and try to only buy them when they are on promotion;
- IP is for buying things that only IP can buy, period. Do it another way and it's really not to your advantage;
- If you want to take a boost do so. If you play more than 2 games a day, take the 30days boost. But spend all that IP on runes (see 1.)