I believe this has been a trend for the last few years and some parts of NJ are seeing astronomical appreciation because of it. 

If there is anything in decent shape just leave it by the curb for a few days and see if it disappears but if you leave it too long you might have an issue with the city. 

There are neighborhoods where I live where all the yards and professionally maintained, and others where every house is in bad shape.  

Should I expect this trend to continue in the future?

Short of a global political cristis or a monetary system issue we should be in good shape: lending standards are still very strict (compared to pre 2008), but have eased up enough to allow for a growing market. 

Even if the prop they're marketing is done up like christmas, if it's in a C neighborhood, no one will pay B+/A rents to live in that area, regardless of what the house looks like.Now, all that said, there are some market trends that you can't see in the numbers, which is where having someone who lives and works in the market you're considering is crucial.

I can’t keep track of trends or spending if I do not have the data.

Does anyone know what a trend/time table of those areas being built and will it eventually be a good location for rental properties?

The main concern of any market where you want to set up a rental property is the population trends(more possible renters) and job outlook (is the city losing jobs which means a probable population decline as mentioned is important  as well as less reliable tenants to choose from).

And you can see when an area is trending up or down, especially if you visit it over time and take good notes.People love tech, and I do too.