why is an amp so important? differences?

Why is an amp so important? I've seen $50 500W amps on eBay and strangely, a 300W 5.1channel (500W total) amp for 500.00 ...so I was just curious, what makes an amp so important? What differences will I hear when I try using a Alpine 500W Amp vs a Infiniti Kappa Five Amp? I was thinking about getting this: http://subthump.com/Chevrolet-GMC-Sub-Boxes/Camaro-2010-Up/Stealth-Sub-Complete-Packages/2010-Up-Camaro-Coupe-12-Integrated-AmpSubStealth-Enclosure-New-clone.html But it is REALLY expensive. A guy at bestbuy told me that I can get a Alpine 500W amp (same wattage as the infiniti kappa five) and save about 400.00 The Kit Im looking at has: (1) 5th Gen. Large Driver's Side Stealth Enclosure With Built-In Amp Rack And Cover Plate (1)5th Gen Factory Amp Replacement Kit (1) Infinity KappaFive 5 Channel Amp 50w x 4 @ 4ohms plus 300w x 1 @ 2ohms (1) Infinity Reference 12" dual 4ohm Sub Power, ground, fuse, rca cables included Is it worth it you think? I've used a Aline 500W amp in the past and I thought it sounded alright. Will there be a difference?

It's about the same difference as different sized cars of the same size or capacity. Or an Alpine vs an AudioSonic. Plus 500W may be RMS, or Music Power (250W RMS) or some arbitrary rating (from 20W RMS to 200W RMS). The differences are only important if it matters to you.

If you're asking what makes one amp more expensive than another, there are many reasons, but the main reason os quality.  Better amps (not always more expensive, but better) are made with higher quality components and are better designed for thermal management, the specifications are real and the amp has been certified to a known testing standard, etc.  They last longer, and more importantly they sound better, offering lower distortion at higher power levels.  You generally pay more for better quality amps because they cost more to build.  Higher cost does not always mean "better" - sometimes you pay more for a brand name - but generally speaking a better quality amp will cost more.Support the12volt.com

without looking at your link i would say that whatever you were looking at is expensive because it is for a new camaro. EVERYTHING anybody makes for a new camaro is expensive as hell. its called marketing.