Nothing about a computer is an investment.
Tell that to all of these companies investing in tools(computers) for their employees
Every single one of your analogies has been horrible. Yes, dig a well before you need it. But don't install a $1000....
I'm talking about preventing a possible problem with the laptop. It's not a life altering decision to go with what is becoming the standard amount of ram in laptops these days.
4GB of RAM is still enough for a lot of people. 8GB is plenty for most. 16GB is needed for a few. Unused RAM is wasted RAM. If you don't think you'll need it in the next couple of years, it isn't worth spending money on right now.
If 4gb is enough then maybe a netbook would be a better option than to buy a MacBook? Would save a ton of money.