After more than doubling my income in said job over the last year (having started as an intern), I repeatedly find myself looking for loft apartments twice the rent of my current place (where I actually like living), unnecessary modifications for my car and the like. 

Account Closed, The TCJA would probably not affect this - but I say probably because this whole thing has become on of the greatest examples of reverse engineering I've ever seen. 

I'm wondering what king of creative strategies for consistently digging up off-market properties are affective for trying appeal to investors?

Then I would repeat with the now 400k for another 10.

This drastically affects the max LTV (Loan to Value) that the bank will give you on your equity.

Once they move out, rinse and repeat until you've upgraded the majority, if not all.

Rinse and repeat.

It is not affected by the passive loss rules.

Also how may this affect experienced investors? 

They can attract a lower quality of customer and the homeless population, though, which could affect other businesses in the center if it isn't managed well.