Nope, you're not seeing things. The font has certainly changed, and I noticed this Monday evening and initially thought my browser was to blame. As a comparison, here's a quick preview showing your post in both fonts:
  (Imported into a page I had saved locally from February.)
Unmistakably the font appears the same style but stretched/raised vertically. Not sure of everyone else's opinions on this, but I think it now appears less clear, especially for certain letters. Although visually larger in size, there's less definition and it's not as legible IMO, especially for lengthy paragraphs. The font used is called Roboto, and is available on Google Fonts listed here. Simtropolis seemingly uses this through reference inside a style sheet (as a web font). The style is 14px regular, which can be recreated using the sample on that listing.
Now interestingly, checking the CSS from my archived page and that which is currently used, there's a small but notable difference: Old: url( format('woff2'); New: url( format('woff2');   The old code makes reference to a version 15 of the font, while it now refers to version 16. Now, it's not clear whether this change occurred this week, or any of the weeks prior. But based on this, there's a strong possibility the font has been automatically 'upgraded' without our approval. There have been no recent theme changes made on-site to my knowledge, in which case this has come completely unexpected.
I'll check with Dirk to see whether reverting is an option. The old version still seems to be online (by visiting that URL), so that may be a possibility. Or if everyone's happy we can always keep with the new version. Maybe it'll just take some getting used to. Any thoughts on this? Maybe another referendum beckons...