How easy is it to quantify the negative value of additional (possibly unnecessary) folders and subfolders in a URL?

[DimasoftTeam]

This post is deleted!

[EGOL]

How easy is it to quantify...

This can not be quantified.  Not by anyone outside of Google and probably not by anybody inside without a lot of assumptions and math.

I am a math guy, but long ago I gave up on SEO quantification.   Not worth the time.  Just do your best.

Working on the principle that shorter is better I would like to see the URL looking more like this:  domain.com/letterhead_printing

Yes, get those generic undescriptive words out of there.  Make the URL short enough that it will be easily read in the SERPs.  Don't clutter with BS.   Use hypens instead of underscores

domain.com/letterhead-printing/

Can anyone tell me how big a difference that would actually make?

Nobody can tell you any thing more than a guess...  My guess is:  Very little for ranking.   It could bring a few more clicks in the SERPs, but just a few.

You have the right idea for doing this properly.  The benefits are tiny tiny (especially in hard competition), but tiny here and tiny there adds up to something that might move you one position higher in a  close fight.