Tell your dad he is wrong. I hate the percentage game but you are clearly right that 80/20 is not the way to go for a balanced system.
I also agree with the statement that the higher up you go on the audio chain, the more that should be spent on upstream components. My current system ($7000 or so) is 22% speakers, 32% amp, 25% CDP, 15% preamp, 6% cables (mostly because they are DIY silver cables where I only had to purchase materials).
If you have a limited budget, I would suggest you find a high bang for the buck speaker (maybe a kit like GR Research, a DIY speaker like Bottlehead Straight 8's or maybe something like Magnepan MMG's that they practically give away just to get you hooked) which would then allow you to increase your amp budget, etc.. In my opinion, on a limited budget it would be better to find the highest quality amp (probably an integrated amp, maybe used) and spend a little less on the CDP. I have usually found more improvement in better amps than in better CDP's (maybe this is just me though). Go the DIY route on cables (like Chris Venhaus cables).