@Jonah Slove
I peaked at around 40 properties in 43608.
I have 1 final property as of the writing of this post and the property is under contract to close this week.
So, the best answer I can give it the zip code served its purpose to create income and appreciation for a decade. Factor that with a total-loss fire, half a dozen insurance claims for smaller fires, easily a hundred evictions, a thousand months of uncollected rent, and a shooting in 2010 that is as close to wearing handcuffs as I desire.
If you live in Toledo and are ready to holster up and manage your own portfolio then 43608 has some real potential.
If you are an out of town investor then I fear investments in this neighborhood (and those like it, Toledo has several) will result in an overall portfolio with higher-than expected wear-and-tear, lower resident financial stability directly translating to shorter times between re-leasing events, and I am curious how much higher the values can go (From $60k pre-2009 to $8k when I bough and I am now steadily see $60k listings again...even a $90k one!).
43608 (and the similar single-digit zip codes) fall into the 80/20 rule...stay out of 80% of them and the quality changes with every block. Locals have to drive the neighborhood in order to stay current on the changes and truly it seems that you have to own something profitable before you will go against the norm and buy more. (On Maple Street only about 3 blocks long I owned 12 houses...once I bought into the street I found value and became known as a cash buyer who maintained their properties so my phone rang and I shook hands on the street to keep it ringing.)
Always check ARIES the Lucas County Auditor site. If you are lucky you are buying a mom-and-pop landlord property that has been owned and operated for a long time. If you are not then you will see a ~$10k foreclosure sale, a resale less than a year later to an unwitting out of state investor for $50k, and the current attempt to sell it for $58k to get the current poor bastard out of the deal and cover the cost of the sale.
Be very wary of becoming the next guy holding the hot potato when the economic music stops...I see rent rates have stopped rising and our local MLS shows an increasing number of days on market so I feel the music is slowing.
Hope this helps!