Buddy, whilst the differences between wants and needs can be subtle, it is more important to want what you actually have, than to have what you might want.
These are very wise words. In Scotland I wore a T-shirt that is sold as merchandise for my favourite blog
http://waitbutwhy.com/It reads: "Reality - Expectations = Happiness" ...
https://store.waitbutwhy.com/collections/tank-tops/products/wbw-reality-tankwhich reduces it even further and so makes it so reach even further.
To want something and to get it does never mean you get happier.
With ownership and choice come the plagues of loss protection and having to choose.
A friend of mine put it this way: "Every lens you add to your bag will devalue all other lenses you already own"
He had all there is to have in Hasselblad, Linhof, Sinar, Leica and Nikon. He sold all but one body and three lenses.
You say that the FM2 and the D3 make you happy? Very good. I feel a reliable tool is worth every cent you spent on it.
When people come to me and ask I tell them to better buy used professional equipment in good shape than new plastic fantastic.
My argument is to better get a used Mercedes than a new Fiat/Ranault/Dacia.
What does one win?
A reliable tool simply melts into the background because it does what it is expected to do. Period.
A lens you often use gains value, because with training you get better and better.
Which lens this might be depends just on your own style of shooting.
Sharing equipment is always fun, sharing equiment with your loved ones? How much better can life be?
Money is no solution, money is just a method and a tool. As overvalued as many other things.