Well, you know, due to differences in xenobiotic metabolism and target tissue responsiveness, you're right, there are times where one simply needs a higher dose (or dosage) to achieve an effect that most others would when given much less.
Though, you're right again, giving a blanket statement that people should take more just isn't smart.
I've found that in certain cases, there are people who have been using/abusing stimulants for years and in such cases, would be better off addressing their "addiction" and taking a long-needed break.
Though again, there are others that I mentioned first who never have and never will respond at a given dose that most others will. The problem however is that figuring out exactly where the problem resides and working to balance it so to speak, would require some rather crude methods (i.e., considering capabilities and resources of the average person) that could be potentially dangerous. One day, many may be able to list the functionality of their major CYP isoenzymes, amongst other things, but until then, if you aren't responding to something at the recommended dosage, I'd consider the possible side effects of taking more or consider not using it.
Hope that helps some.