Also consider adding higher end finishes in the bathroom(s).

For example , the rental amount doesn’t depend on number of bathrooms, garage, basement status or property size.

Finished basement as well with additional room (and has the additional bathroom). 

Planning to start a complete home remodel (interior/exterior) on a home (currently 837 sq ft), kitchen and bathroom bump out, and add an additional bathroom. 

New roof, exterior painting, new flooring, bathroom updates, finished new living space What was the outcome?

I recently added a half bath were half bathrooms add $50k of value

Added a bathroom and remodeled existing.Opened kitchen to diningNew roof, driveway, windows and mechanicalsRefreshed landscaping, hardwood floors and paintWhat was the outcome?

You can get some estimates from contractors for what they charge for big ticket items like to renovate a bathroom, renovate a kitchen, replace the furnace, replace the roof, etc.All wholesale deals should have free and clear title and you should be able to see the sales agreement before submitting the earnest money deposit.

Every time they smoked in their bathroom, they would turn on the vent to get the smoke out which in turn made my whole apartment smell like a ganja lab.

Meaning you may be able to do some cosmetic or smaller renovations like bathrooms or kitchens in your duplex when the tenants turn over and those smaller investments can demand higher rents, so in the longterm you may have more cashflow from the duplex to help fund a future investment in another property while you wait for market conditions to change.