How much does power amplifier really matter comparing to other hi-fi components?

In my experience this is impossible to determine. I currently use an Audiolab 6000CDT with Denifrips Ares ii total recommended retail cost AUD$2300, with Audio Physic speakers and 2 subwoofers RRP cost AUD$9500 and Vincent pre / power amp at RRP AUD$4800. So that's roughly speakers 60%, amps 30% and CD / Dac 10%. The fact is I got the speaker / subs for $4800, the amps for AUD$2600 and the CD / Dac for AUD$2000 so actual was nearer 50%, 25% and 25%.  So $ spend is what I aimed for looking at the market and how they each performed and matched. So the ratio depends on the equipment and deals you can get. I have always found bargains in speakers and never paid more than 60% of RRP. In this case my electronics were a rare bargain both open box but clearly never used (both sealed inside boxes) whereas the CD I bought because its great value anyway as was the dac getting about 15% off each. My second system is Audio Physic speakers list AUD$3000, paid AUD$1000 boxed and new (4 years old left at back of warehouse by mistake when they moved store), Naim Unitilite  (pre / power / CD/ Streamer / DAC / tuner) ex demo list AUD$4500 paid AUD $2500. So that's originally a 60/40 split at $7000 becoming roughly a 75/25 split on paid price. So making up a fixed percentage is just not possible if you are searching the market as you may buy separates or combined components as applicable/ available.