This got me to thinking, with ductwork/wiring/etc already done is simply swapping out/upgrading the unit doable by a moderately handy person such as myself? 

With buying a multifamily rental (house hack), the extra rental income would offset the cost of your mortgage, allowing you to save more for other investments or use it to make upgrades to the property to charge more for rent if the market will support it.

Is dumping 4-7K on upgrades - that may not be even necessary - going to warrant the 100 dollar return on your investment?

Ideally you will be able to do some upgrades and push rental rates even higher.Some new landlords opt to raise rents slowly over time but all this does is cost you more over the long term than having some tenant turn over.

I've recently jumped back into BP, upgraded to Pro - and am actively involved in the 90 Day Challenge.

I've got friends that live there for good rent rates while they're finishing up grad school, but mostly it's blue-collar families taking advantage of living that's even more affordable than OKC! 

Knowing that I would have to upgrade if they ever left to stay competitive in that market, I decided to install granite as a surprise while they were living there in hopes of delaying a vacancy. 

. - Provide utility cost information- Provide receipts of completed work for upgrades or improvementsEven if you decide to sell with tenants in place, issue your tenants proper notice. 

And hopefully by doing the right upgrades up front you will be able to keep capex under control.

--And finally: if I sell or rent, should I try to upgrade even more (add a pool, update the kitchen, etc) to get a better price?