Unless you spend good money on a radiator tower and are doing extensive overclocking watercooling only has 1 benefit.
less sound in the room (keep in mind i wearing noise cancelling headphones, my tower is ear height less than a foot away and I can't hear a thing)
It's a great side project in order to understand loops and how to setup a system for watercooling however ultimately it isn't worth the cost unless is a hobby thing. I've built 1 watercooled system in my time and it worked flawlessly. I overclocked by about a half ghz and it maintained a temperature i could have obtained through air cooling. Overall build time was about 2 hours and included a small tank reservoir on the bottom of the case. Ran for 2 years without any kind of buildup in the pipes.
*edited to ensure sanity*