Having an amp with more power capability than your speakers can handle is not a problem. It's like having a car with a lot of horsepower. Sure, you can go a lot faster than the speed limit. But you won't get a ticket unless you press the gas pedal too far down (or volume knob too far up)! If you're not hearing audible distortion from your speakers, you are probably OK.
And, as someone else noted, you are actually more likely to blow a tweeter by pushing an under-powered amp into clipping, than by applying a lot of clean power. The reason why clipping causes tweeters to fry is that a flat-topped (i.e. clipped) sine wave is equivalent to the original sine wave, plus an infinite series of its harmonics (I'm grossly simplifying). So clipping a low frequency (that is normally handled by the woofer) will generate a series of harmonics, some of which will get fed to the tweeter. It is the increased high-frequency energy of these harmonics that ends up putting too much total energy into the tweeter, resulting in thermal problems. A slow-blo fuse in the speaker wire (or directly wired to the tweeter itself) will provide added protection against this happening. (As an aside, the original Large Advent speakers of the late 60's/early 70's suffered somewhat from easily-blown tweeters, and Advent used to provide you with instructions on the right kind of slow-blo fuse to buy.)
