@ClassyJalopy
I didn't have the time to pick this thread apart because I'm super busy right now but I happened to check here tonight and scrolled through.
Here are my thoughts - it depends on your budget. Can you afford a clean 100 or 200 on top of keeping a reliable older built 100 with some flaws? Are you financing or can you find a perfect one that has a title in hand and bring cash? Only you know those answers.
I would not bother selling that car. It has a bunch of nice mods and maintenance done, but with that mileage and condition there is zero rationale in unloading that car. The money you'll get in return for it will be a pittance. It will be like the terrible mistake I made in selling my BMW E30 5-spd years ago (in perfect shape for $3700 at the low point of the E30 values before they skyrocketed). I regret it to this day.
Keep your beater 100 and don't spend money on new mods for it, but keep it running. Find a clean, rust-free 100 or 200 if you can do it. You have to travel. Madison is terrible in winter (but it's a great city and I loved it there) so you have to go look for a clean one. I am in NC and most 200's are still insane prices. Occasionally you find a 100 in clean shape with no rust within a few hours. Most are clapped out though. It took me months and I drove 5 hours at 3 AM with my pregnant wife and existing kid, but it's the price you pay. Keep the one you have and go on the hunt for another one so you can start to gradually move on. You know the writing is on the wall, you started this thread