You can have all the horsepower you can stand, but it won't do you any good if you can't make any of it stick. Focus on traction to make the most out of what you ALREADY have, THEN worry about throwing on nitrous; if you just go throwing juice at it on a totally stock setup and street tires, you're probably going to find yourself running into a wall, or at least getting some horrible times for the amount of time/money invested.
That said, start shopping for DR's or slicks, an extra pair of rims for those, upper and lower
LCA's, and torque box reinforcements. THEN start saving up for the power adder goodies. You could try running nitrous on the stock gears and see if that works out better for you, as getting too much gear can actually hurt you in the 1/4 mile (hence my crappy 15.0 @ 98 MPH / 2.2 60' time with 4.10's on a fairly stock notch - I can't get diddly for grip, and I'm already just about out of gear when I hit the traps).
A stock H/C/I Fox with proper weight reduction and a good
suspension/traction setup will probably smoke a Fox with H/C/I AND nitrous if he's running street radials and OEM junk
suspension. Wouldn't it feel kinda embarrassing to get whooped by someone with about $600 in mods to an otherwise stock car when you've been pouring cash strictly into making power?