Visualizing all those things in detail on a daily basis keeps me going even when I feel too tired to go another day.

I'd look into the possibility of installing heat pumps with electric heating elements for very cold days(one per unit, hopefully, in the units which currently have electric heat) these can be installed in the window much like typical air conditioners and they will function as air conditioners in the summer- some can be installed through the wall.

I then used the IRR function and it came out with a 19% return.  

It would add some visual interest and make your duplex stand out.  

A good offer is a function of utility, scarcity, business plan, and other things.

$500 here $500 there certainly adds up, but the kitchen is a huge area of focus for buyers, so it'll be worth it vs. a $500 closet system or $500 tile upgrade in the entryway.Also, its my opinion and experience that most buyers (and therefore the market force) don't look at functionality - they look at flash.

I was wondering if it would be considered self dealing if I hired my daughter's LLC to perform property management functions on investment property held within my Solo 401K? 

Cap rate is a market function... it's cash on cash is what they are thinking...

As an investor your profit/gain is a function of one of two things (c) principal amount of loan and (d) interest accrued.  

A fair price is a function of competition.