Other ways to look at it:  if a duplex has a better cap-rate does it suddenly devalue your SFR?  

Although generating positive cash flow should always be the primary source of profit, you can almost be sure that NJ property will consistently appreciate over time and there is much less chance of devaluation compared to more rural areas.

If you think you have a claim against you title insurance you better hope it is not an issue a survey would have disclosed or they will NOT pay your claim and will be stuck with a devalued and in very extreme cases worthless piece of property.

What are your thoughts on having equity as a safety net for devaluation?

You will make more money listing with a agent even after fees.I suggest you get rid of your tenant before you list as they will devalue the property.

Additionally you want to keep it at market to insure your property is not devalued when you sell if it is anything other than a SFH.

That last sentence is not meant to demean or devalue the advice you'll find here on BP or the myriad books that have been published to give someone like yourself well-honed advice.  

I really do not think that will have a big effect and it could even be negative I hear the mayor talk about the massive road contruction  plans and it might even devalue some of the properties The reason hidden by new overpasses and walls noise , etc 

It can devalue your property.  

Fort Myers was significantly de-valued in 2009-2012.