Levels of aggressiveness should not be measured in absolute terms, but instead within the amount of discretionary income that you have, and so yeah a person with higher income could buy more BTC but that does not necessarily make him more aggressive than someone with lower income and who might be using all of his discretionary income to buy BTC. Maybe we can take some extreme examples.
One guy has $100 per month of discretionary income and he uses all of it to buy BTC.. This guy is quite aggressive and maybe even bordering on over aggressiveness (especially if he miscalculates his expenses or if he does not have reserves in place).
Another guy has $2k per month of discretionary income and he invests around $100 per week into bitcoin, which might be considered moderate and maybe even whimpy.
Well i total agree with you and I love the example you gave below, aggressive Investment is not only putting all your funds in bitcoin without having reserved and emergency, sometimes investing %70 of your fund in bitcoin without considering the level of your discretionary and emergency fund can as well be seen as aggressive. if you received $1500 and you invest $300 each every week, making a total of $900 per month left with $600, that is a bad aggressive Investment and surely the person is over doing it. because your bitcoin Investment should be done in a manner that you will not over do it. It will definitely affect you or Put you in a tight corner. If you Invest $900 on bitcoin how much will you use for feeding and running family expenses? Or how much will you set aside for emergency and reserved? Surely if you over invest in Bitcoin, the $600 available amount you will not be enough for emergency and reserved. Definitely it will affect your bitcoin HODLing. Though it depends on you and how you can be able to manage your family. If its you alone you can cope but if it's a large family I doubt if you can manage. The point of the matter is that don't over invest what you can not afford to lose that will make you to sell you bitcoin HODLing down the road because of not having a discretionary fund to back you up.
You can invest aggressively when you have the funds to do that, the most important thing is that you don't over do it, if not it will affect you, and you will end up selling some part of your bitcoin to cover up some emergencies that will arise. Your emergency funds should be in a good condition because that is what will determine how aggressive you will be in buying either monthly or weekly.
Let me start by correcting you, if some one invest $300 every week, in a month time the person will spend a total of $1,200 and not $900 as we have 4 weeks that makes up a month.
Going further with what you said earlier, it all depends on the size of your family and the region you are living, there are some people who can survive with $200 monthly. If you have a small family surviving with $600 will be enough, and this $600 dollars some people can still allocate like $200 into their emergency funds account. See if you want to build for the future there are certain sacrifices you have to make, you have to cut down on some certain things you know you can do with and only get those things you know you can't survive the month without it. We make investment to secure our future, so and doing that there are certain things you have to let go like clubbing every weekend and spending money on hard drugs, women, if you can be able to control your spending on these things I mentioned above you will see that $600 will be enough to carry you for a month, even if you have a family of 3 or 4. Like I said earlier, it all depends on your country of residence.