Amplifier specs, does they matter?

I would never purchase any audio gear just based on specs but as Almarg mentioned they shouldn't all be totally ignored either. Without question, the final judgement should and will be placed on careful listening tests, believe your ears!

Of course they matter, how can anyone say otherwise. Input/output impedance, input sensitivity, gain, number of channels, dimensions, operating voltage, number and type of inputs and color are all critical information. The information won't tell you how the amp will sound, but it will tell if it can operate properly in your system.

Probably the first specification I will look into, is the Watts/channel in 8/4/2 Ohms to validate if power doubles when impedance goes down by half. This will give you a good indication that the amp will not suffer when the speaker impedance varies at different frequencies.

Second spec would be the power transformer kVA specification and total Microfarads of power supply filter capacitors. Again the bigger, the better since it provides an indication of the theorical power handling capability and reserve the amp will have under peak power musical crescendo.

Signal-to-noise ratio would be the last. The higher the figure, better the amp will reproduce clearly low-level details that could hang down near the amp noise floor.

These 3 specifications are nice to have to kind of help you build a mental picture of the seriousness of the amp design especially if you are running innefficient speakers that sound really great.

But at the end, it will be my ears who will prevail regarding the final purchase decision. I will never purchase an amp with excellent specifications which sounds average. I will always go for the best sounding amp with my speakers, regardless of specifications.

Some specs matter to me, specs like size, weight, power output and input impedance are important to me for system matching purposes.
Frequency response, THD, slew rate, and signal to noise specs I do not pay much attention to. Listening will tell me all I need to know here.

Dasign, I would stay away from amplifier that exactly doubles power because in order for this to happen power supply has to be strong enough while output has to be "tightly regulated" which is another word for the "deep negative feedback". In addition many new amplifiers have small amount of power supply caps and tiny transformers since they use ultra quiet line/load regulated SMPS.