After three months of using S2 with the stock 1650mAh battery I decided to buy this 2Ah one, it cost about $20. The battery life has sure been encreased, but the 350mAh added don't do much. My situation about using phone is just like the yours (many friends playing, especially), and I still have to recharge it daily. But now it can last at least untill I come home
(maybe 3 hours of playing Dead Trigger instead of 2,5 before..).
Sure advantage: you are going to have two batteries with 3650mAh in sum, not bad
Conclusion: You will realize the increase of battery capacity, but you will be disappointed how low it is.