I'd love to see currency represented in the full range of D&D coins. At the very least silver, gold, and platinum.
Also, why does it have to take up an inventory slot?
I think something like WoW's model for currency would be almost ideal.
You asking more realistic currency model, but also complain about it taking space? You know, 10,000 coins takes lots of space.... and actually damn heavy (much heavier than it's represented in game).
You're right, regarding realistic use of space. Of course.
My thoughts however, mostly pertain to flavour and convenience. The inventory is already crazy busy with fruit, garlic (?), a million keys, books, notes, scrolls... Now i know that it's my fault for picking it all up in the first place, but alas, i still like the idea of having more than just gold coins.
If the different coins need to take up space too, so be it. I'll get a bag for them!
... I really should use bags more...