There are also people spending more on their headphone cables then the actual headphones themselves.
Yes, the advice works quite well for lower budgets IMO.
It also depends on the gear itself.
Buy a crappy headphone and no amp will be able to make it shine regardless how much money you throw at it.
You should audition headphones (if possible) with familiar music and buy the best sounding one to YOUR ears
is comfortable to YOU and is within your budget.
Then buy a Magni and you're set.
After a while you get the 'upgrade fever' or read that X is sooo much better than what you have and you're done for...
Good sound doesn't have to be expensive.... then the law of diminshing returns kicks in depending on the budget.