10-09-15: Danoroosorry but i strongly disagree.
In the sense that an amplifier is a fundamental and necessary component to any audio system, they are important. As far as it's contribution to the quality of the sonic signature the system produces, provided it is functioning properly and is of adequate power to properly drive the speakers attached to it....not so important. I would think components' affect on sound quality ranks something like this:
do not underestimate the amp-speaker electrical interface. many people here on Audiogon (& other places) have gotten themselves into loads of trouble both electrically & sonically by blowing this off.
The amp is a major part. You get this interface wrong & all your hard work for the components upstream is flushed down the toilet.