Is there a magic formula for spending on components in a system

The percentages in the magic formula change according to the size of your overall budget.  One size doesn't fit all.

It is true that, all else aside, it will cost more to get extended quality bass and quite a bit more for that in a large room compared to small.

That is because the amp and speakers both must work much harder to deliver extended bass and even more so for bigger rooms. 

I forgot to add in laptop and mic for measurements. Most already have a laptop and you can get a good mic for $75. You might need more for Room than I spent. My room was already pretty dampened and restricted on what all I can do since it isn't dedicated. IMO speakers and room are your most important considerations. Invest the most in speakers you like it's easier to upgrade the other items unless you have enough money to get everything you want at once. 

For my system.
1. Speakers $10,000
2. amplification including DAC $4000
3 .Source digital <$1000
4. cables<$200
5. Room $300

Is there a magic formula for spending on components in a system?  Even better: there are many such formulas, each with its adherents. And each formula is right for someone.

In other words, I agree with @almarg on this.

I agree with those above who stated there are too many variables. 
The greatest ones are your total budget and the efficiency of your speakers.  I have two sets of Magnepan and ended up spending a lot more on power amps than I would have spent on efficient speakers.  
However,  for the past 25 years, I appear to be addicted to Maggies.