First as you said there are diffrent ways to set your nitrious up. A spoolup kit will log off before you max max power you might get a little from cooling after the log off but no real power gains. If you spray on top of boost(like me haha) then you will see the power on the dyno. As to why people dont dyno with NOS? some say its cheating but I didnt know street racing had rules?
As for wet or dry neither are in your fuel system. Wet is simply nitrious and fuel are both injected at the same time thru the same jets. Dry (although its not realy dry) is simply only NOS the fuel is added thru inj or in some cases not at all.