¥1,000 (add 8% domestic consumption tax in Japan) – about US$10 – for 50ml wasn't exactly expensive; ¥1,000 (+tax) for 20ml is a different matter.
Only if you want sheen from your handwriting on photocopied (or laser-printed) work documents, and then presumably only for personal satisfaction and/or enjoyment, as opposed to wanting your boss to notice and show appreciation. I have from time to time enjoyed marking up draft documents (because final versions are usually stored and distributed electronically anyway) using a $1,000 pen and 'expensive' inks as a personal idiosyncrasy, but then the nuance would be for my benefit only. I also have a stash of 'expensive' paper (by which I don't mean Tomoe River, since I don't have a high regard for it, but just 120gm coated papers from regular stationers), bought at my personal expense, on which to print my desk copies of stuff to which I would refer from time to time.
Showing sheen, shading, or any other attribute of the use of fountain pens and inks on somebody else's copy is really not something I'd worry about, but then I don't speak for everyone else, so I sincerely ask: Is that a concern of yours, that you want office documents printed on office-quality paper to allow you to show your handwriting (or 'fountain pen art') flair?
I love your "personal idiosyncrasy". I dont have a $1,000 pen, so far my most expensive pens have cost me around $150-225, but I like doing similar things at work. Because of it I found out that my favourite colleague / immediate boss was also into fountain pens, inks and notebooks - she's into all things stationery, actually.
Why do you not regard Tomoe River highly? The 120g paper you are talking about, is it similar to the 90g Clairefontaine?