This is just plain wrong. People change, and their computing needs change. For instance, I bought my iMac three years ago. Back then I needed it for basic home use, iPhoto and that sort of stuff, plus I wanted it to double as an external display for my PC that I used for work.
Well, fast forward three years, I now find myself looking at self-employment, and need a development server for Sharepoint, Dynamics and Service Center. Well, I was negotiating prices with HP and Dell for their small business servers when I realized that what I really need is something with a minimum of 32 GB RAM that can run 3-4 Windows VM's somewhat nicely. And hey presto, take out the 4 x 2 GB modules from my iMac and replace them with 4 x 8 GB modules and I have just that. So, being able to upgrade to make the computer suit my current needs saved me a lot of money. And since upgrades are out of the question with ne new retina mqcbooks, maxing it out *might* do the same for OP a few years down the road.
So, my advice still stands. If you can afford it and think that you might want it, just go for it. As for maxing out everything else, well, your call. It's just that it is easy to stick an external disk in a USB-port or use cloud storage if you need more disk space and the difference between a baseline and maxed out CPU will not be that significant in three years time. Having too little RAM might however make it impossible to run some piece of software, whereas a slow CPU just makes it a bit more tedious. Also, you really can't have "too much RAM", since the OS will aleays use it for something, such as I/O cacheing and whatnot. Whereas if you spend megabucks on a huge SSD that never gets more than 25 % usage you have effectively wasted your money. Sure, in light use the difference between 8 and 16 GB RAM might be so small that it is basically not even measureable, but it would still be there...