They spend a ton of money on advertising their product and apparently have none left over to spend on product development.

I remember reading something in the Wall Street Journal the other day that buyers lean toward modern finishes with a nod toward sustainable materials.

Also, staging and professional photography can help potential buyers visualize the space better.Lastly, think about local advertising—social media, networking, and maybe hosting an event for local agents could help get more eyes on the property.

My company has just grown organically - we've never advertised per se. 

The fact that your property manager only advertises on Zillow is worrisome.

Effort is still required to communicate with the Craigslist advertisers, but having software to lift the deals out of Craigslist would surely be worth $1,000. 

Better materials such as stronger  lumber were used when the earlier vintage properties were built and many  contained design characteristics such as stone or brick work and intricate millwork that are too costly to replicate today meaning many buildings are significantly below todays replacement cost. 

My brokerage would employ data-driven pricing guidance (hard to see how this would be materially different from MLS comp sheets; perhaps more accurate).

So spend NO money on advertising and use that money to make our product stand out.. this has led us to raise our prices Far above our competition more than makes up for it and we sell them as fast as we can build them.. for us thats delivering 2.5 homes per month. 

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.