Are you me?
I just went through this situation recently. I'm in the same boat you are in that I live in such a walk and public transportation friendly area that I don't even bike all that much. I also work from home 90% of the time. But I had the yearning for a second bike. And my rational was that I had stopped riding over winters because I got rid of my worn down beater bike 3-4 years ago. Little winter riding eventually led to little riding in general. I also have a sentimental attachment to my road bike (my first new bike that I paid for ). I'm not super comfortable riding it in the winter and/or bad weather too. Used to ride in the winter when I was younger, but am a little more prudent now that I'm heading towards dotage ;) It has 25mm tires and can't be bumped any more than 28mm. I have over the years, transformed the roadie to be more commuter friendly, but can't do much about the narrow tires.
Due to my apartment situation and limited storage, I couldn't buy another mountain beater bike--unless I left it outside. I live in a fairly low-crime neighborhood but leaving a bike outside on a full time basis is anathema to me. No matter how low-rent it is. Plus, my apartment building doesn't have bike racks/parking. So not only would it have to be outside, it would have to be locked out on the sidewalk.
Long story short, I focused (more like, obsessed over) on buying a folding bike. I had a spot in the living room for a tidy folded up bike. Yes, they have smaller wheels but many use wider tires. I bought a new one for over $700 but that was a bit of fiasco and I was able to return it with a full refund plus shipping costs. I then parked myself on Craigslist until I found the right folding bike for the right price. I bought a Dahon 20 inch wheel bike for $150. That took about a month. The tires are 1.75in width so I'm hoping it will be sturdy enough for crappy road conditions. I stuck a small basket on the rear rack (the bike still folds pretty well!) and that makes it a proper town bike now :)
So yeah, if you want to dip your toes into a 2nd bike territory, especially one for hardy commuting, they're pretty easy to find on CL (making big assumption you have CL in your area). If I can find a folding bike--finding old hardy steel mountain bikes will be a breeze. A whole bunch of Trek 800's out there. There's also eBay. I bought my old beater bike off eBay for $40 and then spent about $100 for a tune-up and miscellaneous upgrades. That was 12 years ago.
I'm paranoid about bike theft so it's a bit of a relief to have an older used bike that I can leave around town. If it's the beater bike, it's going to be used and left all over town.
But...if you want a new bike...go for it. I bought my roadie for $500 14 years ago. At the time, it was such a big purchase. Well, 14 years later, I think that $500 wasn't a bad expenditure at all.