For math? Yes, it does not matter as long as the scaling works.
For human mind? No, it does matter! The majority cannot handle big numbers. For example, they understand the difference between 10 and 20. But when it comes to big numbers, this does not working anymore. People start to shorten numbers (instead of 10.000 they say 10k). But the problem is every bit counts. 12.499 and 24.998 have the same relation as 10 and 20, but peope shorten these numbers to 12k and 25k and now it's nowhere 1:2 relation.
So yes, big numbers do affect players negatively as they cannot handle them right.
Nope. Gold and silver are just multipliers. Base money unit IS copper.
A quest that rewards you 500 gold, in reality rewards you 5.000.000 base money units.
Gold and silver exists pretty much only to crunch the numbers to something manageable, because without them we'd operate with millions even in vanilla wow. Today it would be billions.
The method you described works in a game like Tibia where you have gold, platinum and crystal coins, with same value ratios (1 cr = 100 plat; 1 plat = 100 gold. therefore 1 cr = 10000 gold). But currency there isn't actually a currency. It's an item that you keep in your bag. It stacks up to 100 in one slot. Therefore, gold; crystal and platinum coins have different item ID's - they are actual stackable items, not just currency.
Also when the squish was happening Blizz stated outright that they intentionally did not squish HP as much as damage.
The reason for this was obvious to anyone who did PVP: Players in MoP could do single hits on mobs for double or quintuple a player's health pool, so PVP required massive base resilience to lower damage enough so that players weren't one-shotting each other. By letting HP go higher relative to damage, players no longer needed ~50% base resilience at all times.
I think something that would be good is drop stamina and replace it with a damage reduction type thing that only works in PvE instances or world bosses. As you progress through raids/dungeons and get better gear players will take the same amount of damage, but the damage itself will be higher so that you can bring a fresh 110 in as they'll get one shot, kind of like resistance gear.
On the flip side it's a terrible idea due to the way spell power scales for healers. In the beginning of the xpac it'll take 5-6 flash heals to fully bring up a target and at the end it's around 1-2 depending on your spec. That would need to be addressed as well. Maybe have healing be in % rather than a flat number?
That's one of the few situations in which they have total and absolute control over the balance and it's strange it falls apart like that. In WoD, there's no reforging, gems are weak, non-weapon enchants are just a slight boost, and they know exactly what flask you'll be using, so it doesn't make sense that they would double the value of stamina but still not manage to prevent spellpower+secondary creep from catching up. I mean, they have 11 years to work on it and employ people with degrees in math just to work on this and yet... you're not wrong.
Soothing Mist:"Healing them for a minor amount every 0.5 sec, until you take any other action."
Jade Serpent Statue: "The statue will also begin casting Soothing Mist on your target. healing for 50% as much as yours. "
[What's half of minor?]
"Statue casts Soothing Mist at a nearby ally for toddler healing."