FWIW, I wouldn't worry about the inspection part with NOS. The fogger nozzle gets installed in the intake somewhere, and you can either do a really good job of hiding it, or just take out the nozzle and lines when you go in for your inspection. It may be minorly annoying, but your talking maybe a half hours worth of work once a year... not bad at all. If you get pulled over and they pop your trunk and see the bottle hooked up though, that could be trouble. Here in MA, I believe that you weren't allowed to have the bottle connected while driving on the street, but I don't know of anyone ever getting cited for it. I don't agree with the statement that it's only good for the strip. Set up with some of the extras makes it easy to turn on/off on demand.
As for using it, yes, it does get very addicting. The major downside to it is refilling bottles. Sometimes it's a pain and it can get expensive if you go through a lot of it. Most basic kits come with just the bottle, lines, and controller unit. A bottle heater to maintain proper bottle pressure is a must if you see temps below 80 degrees. Also, a remote bottle opener is hugely convenient so you can open your bottle without getting out and going in to your trunk. Most kits come with the jets to go up in shot size quite a bit, but 125HP is the practical max if you have a stock fuel system. You will also need an SCT device or something similar so you can pull a couple degrees of timing out of your tune. A window switch also helps make sure that it only sprays in safe RPM ranges.
I had the Zex kit and I still like it for several reasons. One, it automatically adjusts fuel enrichment based on bottle pressure, so you don't have to worry about spraying pig rich if your bottle pressure is low. Two, it has everything built in to one neat little box so it makes the installation pretty clean.
I completely understand where you are coming from as well. I wanted a power adder that was beyond the basic bolt ons but I didn't have enough for a supercharger or turbos. I bought my stuff used off of e-bay for an awesome price, used the crap out of it, than sold it for basically what I paid for it and put the money towards a super charger when I had enough saved up. There are tons of people selling their nitrous stuff. You can easily get a good setup with a lot of the necessary "extras" included for $600 or so. Check out corral froums as well.
Power in Numbers: None of us are as dumb as all of us