One effective strategy to maximize unit potential is to explore opportunities for adding extra units, especially in C-Class properties.

I also agree that RE appreciation is unlikely to match the last dozen years, but you never know.Where I am unsure we agree is that paying $450k to improve the cash flow ~$3k (your numbers but I expect my delta wold be similar meaning both my cash flow estimates would be worse than yours but both would be worse by the same amount not affecting the difference) makes sense especially if the cost of having the extra $450k is only 6% rate which is historically simple to beat via numerous investment options and hopefully no one is investing in RE for an expected of 6%.  

So your saying select No Damage Protection and just submit an extra charge when it's warranted? 

If I sense the buyer is cut from this fabric, I will negotiate extra hard against repairs to the extent they simply walk.

We have increased our monthly rent to price ratio from your ~0.75% to 1.1% but the leverage ate up all the extra cash flow (even if the total return is likely higher).You could be a cash buyer and go from your one property to 20 and cash flow 20000/mo but you are still having to buy and manage 20 properties.You can do better on the total cash flow in other markets or rougher neighborhoods, but the story is similar: you are getting an extra ~25-35% in income for 20x the hassle.

Others investors drive extra ROI by thing like ability to reposition property for greater profitability and or less risk; ability to rehab property at less cost, ability to identify areas where gentrification is likely to occur, etc. 

Insurance is expensive, there is a lot of extra maintenance like painting or electric in common areas that don't apply as much with smaller units. 

It almost feels like they make it difficult on purpose so they get extra revenue on late fees.

Vs her current super-chill life, get's special discounts all over the place for being "too poor" and all the while can work cash jobs when wants extra, keeps her bank account low, plays the game to get here "free ride". 

I think if you have a little extra time, operating a smaller STR business can pick up some good income.