In this IDEAL situation the savings is minimal.  

A property in Boston will appreciate well, but with minimal cashflow.

Yes, you will have to caulk in some places especially around the tub/wall), but it will be very minimal to what a five-piece surround takes.I recommend only two-piece surrounds in full gut rehabs.

My gross income is a bit less than $7k (and I'm renting near top of market rates) with minimal repairs ($2k/y), but...1.

., early retirement, maximizing cash flow, minimizing debt)?

Does not include upkeep which is minimal after year 3.  

I'm reading a book now where the author purchased hundreds per year putting minimal amounts down, that doesn't work anymore.

Board games can be worth it, but I'd keep it minimal - maybe 2-3 family-friendly classics.

I find single ADUs are mostly being added by people with minimal RE investment experience often without a clue as to the value that will be added by the adu addition.  

This approach ensured minimal holding costs and a faster return on investment.