I like the serif font. I get tired of seeing san serif on everything! I think the ubiquity of san serif is a reflection of the web and "devices" - "smart" phones, tablets, etc. (But then, I'm a bit of a "fossil", I guess. I like paper products, hard copy and hardbound books, large paper maps, letterpress printing, calligraphy, and even hand-drawn and hand-lettered maps and other works of art with and on analog media.)
I also like how clean and uncluttered this map looks. Just because there is space is not a reason to add more "stuff", even if it might be interesting and/or useful information and detail.
That's my opinion anyway.
These differences are one reason cartography is an art as well as science/technology.
It's funny you mention paper maps as part of the reason you prefer serif fonts. I actually get my preference for san serif from the same place. Making road maps for CSAA we had type specs for everything and one of the base specs was sans serif for most human or cultural features, serif for most natural or geographic features (especially water). And I'd even argue there is a certain amount of "natural mapping" between serif fonts for natural features and sans for non natural, but that's certainly colored by my own experience and preferences. At any rate the preference can pre date "modern" digital mapping by quite some time.
I agree on not filling white space for no reason, not a good idea. But if there is information that could be added to a map to give it more value it's certainly worth evaluating. I think short histories of some of the bridges or the river itself would be a great addition here, and not just filler.