Cons: It costs money to buy, takes time and knowledge or money to install. If you post vague questions without any background information or data on the machine or type of riding and therefore choose the wrong one for your application you won't like the result.
Dunes like more revs, you're going to want the stage 2. You'll need a set of heavy duty valve springs and if you don't want to lose your bottom end power you're going to want an 11:1 piston thrown in too.
Stock is 100mm, if your engine is old and tired like most of them that are still stock after all this time then you'll want to bore the cylinder and throw in a larger piston. I'd suggest the 101 for two reasons. First it's cheaper than the 102mm, second it's large enough that when you bore the cylinder you'll likely remove enough material to resolve any roundness or wear issues of the cylinder lining.
You would have to measure the cylinder/piston to see if it is still within specification. If it is out then you would want to bore the cylinder. You could put an out of spec piston back in it but you will be spending more $$ in the long run because it is going to start smoking and have power loss much sooner than replacing it.
100mm and 101mm pistons were the same price when I bought a about a month back, so that isn't really of any concern. On the other hand, if you are referring to the boring of your cylinder, that could be a different story, depending on how much a shop is going to charge you. Shouldn't be too outrageous regardless.
You haven't opened up the easiest, cheapest power gain available to you yet - the airbox (and then re-jetting). Next would be a full exhaust (which you're going to need if you work on the piston and cam anyway).
Don't throw money and effort at a piston cam until you see what can be done just with your exhaust and an opened up airbox.
Not all slip-ons are going to fit every header, so it's a chance you take by not buying a complete system. I know that the Powerbomb doesn't make the power that Sparks or the CT makes, not sure how it compares to the Yoshi though.