Each Mod will not necessarily increase performance. The only way you know is with a dyno test after each mod. Sometimes a mod will decrease performance.
Dyno time is expensive and frequently hard to schedule. It's not the ONLY way to accurately see what a mod does. How about a simple $30 or less stopwatch and measure 60-100 mph times? That way you are out of the hold back in 1st and 2nd gear and it is highly accurate, highly repeatable and dirt cheap.
Or you can invest in an accelerometer. G-Tech makes a good one. Might spend $250-300 for one, but you can eat up that much money in just a few dyno pulls and have nothing for your next mod except another bill from your local dyno operator.
I have nothing against dynos. But just like every other power measuring tool, they are not absolute. The results vary widely from machine to machine, from operator to operator and even from day to day on the same machine with the same operator. Ultimately they can only be used to compare a before and after mod on the same day on the same machine by the same operator using the identical setup. They are just about useless as an absolute measure of power or for "bragging rights." Just another tool to be used for their intended purpose.
I've found use of a simple stopwatch on the same road surface in the same direction on 60-100 mph pulls to be just as sensitive and effective as dyno pulls in determining if a mod is increasing power and if I'm headed in the right direction with my mods.
Try it. You can do it any time you have the urge and don't have to schedule time and spend big bucks. With just a little practice you will find your results to be highly reliable and highly repeatable.
Next step up would be an accelerometer. Both also have another advantage over a dyno in that they measure performance changes out there in the real world, on a road with the vehicle being subjected to real world operating conditions such as the effect of aerodynamic drag as speed increases and the flow of air into the front of the car just as will take place under real world conditions rather than all this hood up, hood down, size and location and speed of fans, and correction factors.
It's on the road where the power gains or losses matter, not in a shop with the car strapped down, spinning a drum, out of the effect of wind and aerodynamics and being exposed to electric fans.
Just a thought.