You WILL also have turnovers (i.e. vacancies) that require some degree of investment (re-paint, carpet,fire alarms, light bulbs, etc, etc) and while the vacancies may be short, its not easy to turn over a unit with ZERO downtime.Regarding your planned refi, I assume your 3.75% 30-year is based on an owner occupied mortgage? 

You'll have drywall cracks, so you should factor in drywall repairs and repainting. $$$4.

We added value to this deal by making the following cosmetic changes:- Repainted the entire unit- Updated all outlets and covers to be uniform (a few USB where applicable)- Updated all light switches to 'flat panel'- Updated kitchen cabinet and drawer hardware- New stove & range- New sink outlet- New kitchen ceiling fan- New toilet- Deep clean & high quality post/advertising to emphasize the value the condo has to offer What was the outcome?

We also repainted and generally cleaned the house.

To add to it, once you get the knob and tube out, you can insulate your walls and your unit is now more efficient.Also, since those houses were likely painted and repainted over the years, there is likely to be lead so be careful during any renovations that you or your contractors are taking precautions to the the job safely.

Repainted the exterior and interior of the house.

When it inevitably chips, you'll need to continuously repaint.

For example, in new construction the developer cares about comps so they won't budge on price, but they will give you thousands of dollars worth of gift cards to Home Depot, put in a fence for free, repaint ect particularly if you are one of the first units to sell.

After purchase I installed new flooring throughout, repainted the entire home, updated lighting to LED, updated master bathroom, replaced old furnace, air conditioner, and propane with a energy efficient geothermal system that heats, cools, and heats domestic hot water.

. - total kitchen remodel $15-20K-new washer/dryer $1500- bathroom just needs cosmetic remodel 2K- replace back door $500 (family member works for window and door company and gets a large discount)- furnace is about 20 years old so would need to be replaced soon 3K- possible rewiring of the house (worst case scenario) $7K- repaint.