If you're talking about just a rebuild, you really should tackle it yourself. A blaster engine (except for requiring a few special tools) is about as simple an engine as you can dig into. It has about half the moving parts of a lawnmower....
If you're looking for a performance build, that's a different story. Ken O'Connor put out a series of youtube videos about some basic porting steps that will clean up that poor casting on that blaster engine and will breath some new life into it. His entire video series is about what a regular person can do at home with a simple dremel tool and some carbide burrs, stones, and sanding paper. What he shows in the video is relatively simple and can be done by anyone with a steady enough hand to hold a dremel tool.
Basically, I recommend it to anyone with a stock blaster top end simply to "clean up" the casting flaws.
In order to extract maximum power out an engine, however, more in depth work is necessary. The blaster engine suffers from a lack of exhaust port area(severely from the factory as a matter of fact) and, depending on how you want to tune your engine, the port timing can be modified to change the power delivery characteristics. Couple a portjob with a head rechamber and you actually have an engine that flows better AND burns the available charge better.
Instead of an old 70's tech low power beginner quad, you have a rip roaring snorting 2T.
