Increasing the wattage of a PSU does not affect the performance of any of the components.
Either the PSU supplies sufficient power, or the whole system just fails.
If your existing PSU adaquately powers your machine, upgrading it won't change anything. Having a larger wattage PSU won't make anything run faster, it will only facilitate adding a more power hungry device like a higher end video card.
In my opinion, the difference between a i5 3330 3.2Ghz and a i5 3570 3.8GHz is not worth the money to buy it.
Tom's Hardware recommends that upgrades are only worth it if they move you up about 3 tiers on their chart (page 5 of the link http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-5.html)