raising compression ratio in any piston engine is a great way to increase torque, but it won't create huge increases in horsepower. Horsepower is related to how fast the engine can run, whereas torque is created based on the forces acting on the crankshaft at any point in time.
So anyway, raising compression is useful. However, it's not as simple as just raising it. There are lost of options...some engines are factory-equipped with dish-faced valves, so replacing them with flat-face valves will raise compression. In most engines, the pistons can be changed out and replaced with specialized (or in some cases different factory ones) units that are designed to raise compression (piston application varies with each different engine). The cylinder head and engine block mating surfaces can be machined down to bring the piston further up into the combustion chamber, which will also raise compression. There are other ways, but these are the most common.
Many things have to be considered when raising compression. The reason for doing it is that it creates higher compression temperatures, putting more energy into the compressed fuel/air mixture, thus creating a more powerful explosion when the fuel/air mixture in the cylinder is burned. But, with higher temperatures come other risks. In most cases, higher-octane fuel must be used to prevent premature detonation of the fuel/air mixture. Also, engines with aluminum cylinder heads & blocks are at greater risk of overheating and surface damage if temperatures get too high. Another aspect that most people don't consider is the increased wear on the connecting rod bearings.
let's say, for example, that your engine has a 9.5:1 compression ratio. If you raise the ratio to 10.5:1 (by any of the methods discussed above), the more powerful explosion of fuel/air puts much more force onto the connecting rod bearings and crankshaft. This will accelerate part wear and eventual failure. I'm no expert, but I've heard from many different engine builders that, for a street engine that will be daily driven and raced from time to time, compression ratio should stay at or below 10.5:1 in order to prevent premature bearing failure.
So, those are some pro's and con's of raising compression. Of course, there are many more aspects to look at. I just chose the most obvious ones.
As for blueprinting the exhaust...this is the art of making each exhaust channel of the engine *exactly* the same. exhausts from the factory are pretty close, but of course are not exact. There may be slight differences in tube size, small dents, variations in tube length, variations in bending angles, things like that. When an exhaust is blueprinted, each tube is made identical to each other. This ensures that each cylinder flows exactly the same amount in all RPM ranges, and will improve performance and throttle response because it improves exhaust pulse balance.