Major issues are lack of parking, lack of elevators, leading to numerous unlived in units.  

We have run in to numerous accounts of this.

Search the BP for ADU appraisals to encounter numerous examples.

Sometimes it's ambiguous, but even then, why should I bother with the company that has numerous unresolved lawsuits, versus another company that is virtually the same but has none.

You would be surprised how much Wayfair marks stuff up, and that a lot of things that are marketed as unique are sold by numerous retailers. 

Each exit strategy offers numerous advantages on both sides. 

Quote from @Kevin Rodriguez: After numerous unsuccessful attempts to secure a deal to cohost, I’ve decided to adopt a new strategy.

We have numerous who have their payments set up to auto-pay.

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%.  

Wanted to chime in as I have jumped into numerous courses & attended seminars as well.