12 units at $50 per month for storage is $600 a month, versus the $250 you are expecting for rent from the business down the street.

Of course one condo in Cambridge has a variety of risks -- condo could change rules, there are more and more A+ quality apartments in Cambridge, there could be a trend away from urbanization, etc.The pros and cons of REI versus diversified stocks and bonds is well documented so I won't go into it. 

I challenge you to consider looking at the house split as "a cost of doing business" versus them "giving them or them taking  X amount of dollars". 

Anyone else dealt with this and how do folks draw a line on what is a nice to have versus an expectation? 

Also the way you typed it looks like you made multiple water claims versus one large claim event - if you have multiple claims you'll also have the deductible applied to each one as a separate event.  

Potential Tax benefits aside , I like your ability to be in a position to even have the option of making a choice to pay off your mortgages versus holding them.

Also, be sure that you are seeing the complete listing - some sites like Zillow will sometimes only download part of the listing details from the MLS (if its listed there) and put up some generic county tax photo or streetview image versus what the agent really submitted.Again, if it wasn't for the streetview image, I would give them the benefit of the doubt, but that's just straight lazy.

Adding REI to the end (domainREI) is available though and I will likely be going that direction for $8.99 versus $3k.

This is a WOW of a deal in my eyes for the amount of money invested versus cash flow.  

I would wager that you could do that in a matter of a year (even with seasoning requirements).