You can appeal to potential renters who have extra discretionary income and are willing to pay top dollar for a renovated property. 

I would start with does living in the duplex appeal to you compare to what you could buy for a $250K personal property? 

I see some people in my area buying homes they wouldn't want to own outright simply because the purchase price seems appealing.  

It is possible the $300K house is over assessed and you may be able to appeal and get them lowered.

If they are it probably should be valued as a multi-family property since it will appeal primarily to investors.Is subdividing a potential option?  

Years ago, I read quite a bit about putting up bullet signs and doing short sales, but that honestly didn't appeal to me. 

As for a price to charge for the rent, I would again check the local market for rents and I would think you might be able to get a little higher price on your land because it appeals better to people because it is not in a park.As for selling to the home to the a buyer on payments.  

Personally I plan to have most of my after-tax investments in Real Estate since one of the appeals of Real Estate is the tax treatment. 

In order for them to be appealing to this specific market (city dwellers, deeper pockets, a specific design aesthetic), we could put in about $1k in cosmetic design-related improvements and about a week of work.

The best way to force appreciate a home is through renovations in the kitchen, curb appeal (front and back landscaping), bathrooms, paint (interior and exterior), and flooring.