I found this story from someone on reddit, and I found it so simple, clever, and enthralling I have since retconned it into my world and made it into fact. Hopefully you guys find it as amazing as I did. This was three years ago now, and it's stuck with me that long so I think that's a statement on how good it really is:

The Fighter decided to ask our Wizard why he needs gold to cast a spell on some boots.

What follows is paraphrased from the best answer I've ever heard by a party wizard to such a simple question.

"sigh...Because gold is magic. The first day I was an apprentice, I remember my Maestro asked me the simple question, 'Why can’t we create gold?' I thought it was an odd question, but as he left me alone to think about it, I realized I’d heard of wizards creating fire, summoning water, producing force, and all sorts other of objects and effects... but never of a Wizard just sitting in a tower summoning mounds of gold. You’d think if it was possible, someone would’ve done it by now right? Well...why haven’t they?

It’s because gold is magic. Well, a physical manifestation and metaphysical conduit at the same time, but for your purposes, it is magic. I mean, when you sit and look at the evidence laid out, how could you not have come to the conclusion sooner? Let’s take, oh...dragons, for example. When you imagine a big bad dragon, the next thing you imagine is it guarding its’ hoard. Hoard of what you say? Oh, that’s right, GOLD. Doesn’t it strike you as a little odd that an entity whose literal being is infused with magic just happens to have not only an insatiable, but uncanny magnetism towards large quantities of gold, along with the urge to acquire as much as possible? Possibly Like-Begets-Like, mayhaps?

What about Dwarves? This is a race whose history lies below ground, closest in proximity to the veins and shafts where gold accumulates and grows (Yes, I said grows). Also the only natural race with a strange resistance to magic. Interesting, wouldn’t you say? Almost as if there’s a subtle inoculation against it by such proximity for generations...

Lastly, to get back to what exactly I am doing with all this gold when I’m making your lovely magic item, or all my scrolls...You’re right that I’m not spending thousands of coins upon jewels and masterwork items to hold the magic in place. That’s ludicrous, but if eldritch manipulators are spending money on high end items to imbue, it’s probably a personal focusing preference. For myself though, as you can see, I am working with normal mundane items. As to the details, first I am transmogrifying via prestidigitation these elegant golden coins into their more metaphysically soluble powder form because essence diffusion is easier by an order of magnitude when working with particulates instead of a boatload of Big Ol’ Coins. Next, with a certain amount of forceful application of will and choice incantations, you will notice the gold powder I am sprinkling and kneading on top of the object appears to be being absorbed. Remember what I said about manifestation and conduit? So the gold is not only priming these boots to be receptive towards my spells, but it’s starting to establish a channel to arcane ley lines it order to keep the magic going. And yes, it is indeed very time consuming rubbing gold powder into an item one pinch at a time while maintaining the proper mental focus. There’s a REASON it takes us about eight hours for every thousand gold a magic item requires. You think a consortium of magic users got together and decided on union hours for magic making? Hell no. Its plain, old, tedious, but important work if you want it to function correctly.

Now, master-of-arms and all things armly, would you kindly let me focus on the task at hand so that when I’m done, we don’t have to worry about our Holy Dictator suffering from extreme vomiting and nausea whenever he puts his shoes on because I had to split my attention trying to condense decades of intense arcane study into an elementary discourse?"

Source: /u/C3LM3R, https://www.reddit.com/r/rpg/comments/2n952n/the_fighter_decided_to_ask_our_wizard_why_he/

I like it.

Beautiful.
This is my new official reason for Dragons to be so drawn to gold and Dwarves having resistance to magic :P

yeah I really fell in love with the story and have fully integrated it into my world. So in my world, we're on this cusp of a magic-industrial revolution, and things like airships and single screw steamships powered by magical machines are coming around, and what's the fuel? Powdered gold. It's created a whole slew of pirate story opportunities where finding hoards of gold actually makes real sense lore-wise.

Additionally, it really brought a sense of immersion to the idea that you have to buy magic rather than it being a game-tactic to limit how much magic shit your players can have if they happen to have a wizard in the group.