Water/alcohol injection will do more for you than just lower the air charge temperatures. The most important benefit is it raises the octane of the pump gas that you are using. By doing this, it will eliminate knock caused by detonation, even when increasing your boost. Obviously there is an upper limit though. To figure out if you would benefit, find out if your computer is pulling timing to compensate for higher than stock boost levels or from high intake air temperatures. The computer will try to always output a given max horsepower. This is why when it is cold out, your boost will decrease (unless you can control it), compensating for the denser air which makes more power. With water/alcohol injection, you can significantly raise your boost, and since there is no knock, the computer will not pull timing.
Kits are pretty easy to install, it just consists of mounting the injector(s), and then runing the tubing and wire. The wiring is like installing a stereo, the tough part is making sure it is a clean install and hiding the wires. As long as you have someone to answer your questions, it is a very simple process, and you will see gains. The more mods you have, the more power you will gain.
The main way that people get in trouble is by trying to build a DIY kit. If you know what you are doing, this is can be a great way to go, but most end up buying inadequate parts for the pressures that will be applied to them. The common weaknesses are the tubing and the solenoids. If you do a DIY kit, don't go cheap on those parts, buy something designed for the application.
Also, people get a little to macho and think that alcohol is the secret of the power, and then inject a 80-100% mixture. This is not true, but yet people inject a significant amount of meth (more than 50%, which can actually lead to more knock). If you do get a kit, try straight water first, then 10% methanol, then 20%, and so on, up to 50% max. Most find that around 20-30% works for them, but many people get the most gains from straight water.