I mentionned in another thread that on my "daily camera", wich has a 12MP Sony's sensor (found in Nikons too), when I mount top prime lenses, the sensor seems to be in another league.
Without or before the need of more megapixels, what I've been seeing so far is that to use our sensors to their full potential, whatever that's not top class lens will limit the sensor's capability.
It seems that this fact is also truth on the other side.
So it's a little bit ridiculous being tempted by more megapixels if the lenses are not capable of responding to an increment in resolution.
But that's what happens in most cases. I've been falling in the trap to wanted more MP, but I realised that the first component to take into consideration is the lens quality.
Then, if needed, upgrade the sensor.
Sharpness is not determined always by the lens. A good technique and understanding of many factors are involved.
The thing is that you do not want necessary razor sharpness or maximum resolution, but the important thing IMHO is that when you want it you can.
An equipment is not going to make you a genious of photography, of course, but a regular equipment is not going to help you either, in some cases it can limits you.
Opting for the best gear possible you can buy means peace of mind. Good cameras and lenses gives you what I call: "you don't notice the equipment".
If I notice the camera in action, then this is not a camera for me. I have to be able to forget the gear and concentrate on the task. The equipment has to serve you,
not the opposite. If you are constantly fighting because of the bad design, bad controls, bad tripod etc...
And generally, the gear that respond to this simple law is the high end equipment. There are some bargains like the 5D MK2 or Sony 900 but these are more
exeptions than the rule.
If you deliberatly choose to use inferior gear, as a deliberate and conscient choice, you will be happy. Sometimes it can open creativity, so as the oposite.
I can open new paths using my 3MP mobile phone camera (I do it all the time), but also going LF, learn about that and increase my expression too.
Asking also simple questions as you mentionned: what do I need and why. Then that might leads you to simplify, or to go bigger, heavier and more expensive.
If the choice is conscient and truth, it will always be a good one.