My core book of business is in the shenandoah valley in VA.  

@Nicole W.If you use laminate with a high density core and a wear rating of AC4/AC5 - essentially commercial grade - you should not have wear issues or problems with occasional moisture.

My intuition strongly indicates that the most desireable core areas not only appreciate the fastest, but tend to go down less during recessions.

If you are okay with living in the duplex, let it season some, and, as mentioned, keep saving up for the down payment on the next one while studying the market and expanding your landlording skills--both on the ground with the duplex and with books (I have a Classics of Landlord Lit" blog post, but you may have burned through the core reading). 

My default plan is to "hold forever", unless I have a compelling reason to sell, since my goal is to replace my career income with rental income.

So as population and incomes increase you have to add onto existing buildings or tear down and build with more density and higher to be able to handle and absorb the increase in population.You could have a 10 million Walgreens in urban core.

It didn't compel me to sell my house, but if I was of a mind to sell, I'd have called.

@Ray I do think the urban core looks enticing and it's top on my list to further look into.

My core competency is locating 25-30 good deals for investors a month.

I also have some who are strictly interested in core for other reasons and will take much lower returns.