Better sound

Honestly man, I would save the $$ and get a yourself a full exhaust system. To answer your question, I'd bump my main jet up one size with just a slip-on and ride on.

However, it is not hard to re-jet an engine for an aftermarket pipe, and all the power comes from the pipe, not the silencer. The stock pipe sucks and I agree they sound terrible.

If you get yourself a Toomey, FMF, or DMC exhaust, it will sound great and it is a HUGE improvement in power over stock. Toomey sounds the best, IMO. You can get a good used example of any of these exhausts for under $ 300.00.
 
Troll the for sale section, Ebay, and your local craigslist. Blasters are popular little quads but the single biggest improvment you can make (powerwise) is a pipe and everyone knows it so the used prices reflect that.

There is a Pro circuit platinum pipe and silencer on Craigslist fairly local to me. I thought about buying it and just reselling it on here to help a blaster brother out.
 
Thats a good price. As long as it comes with the flange and everything (which it looks like it does) I'd jump on that. Especially since you posted the link.