If the park is not active has no paying tenants and no cash flow it is worth nothing more than the land value.  

We have a duplex and would like to sell it to buy a house on a 5 acre plot of land.

The less land the better :) bonus points for anyone with commercial experience as her current property includes a commercial building and I have no idea how to evaluate its worth. 

This place is old family land that was sold out and I purchased back into the family.

I am developing some land into a retail commercial building of $19,000SF.

Your depreciation guess seems low unless the land was very valuable compared to the building. 

We have acquired properties in 2 counties for the sole purpose of developing un disturbed lands and retrofitting existing farm then leasing to cultivators.

I did something similar, but used cotton balls and bleach only; I applied it to the moldy caulking — it stayed put really nicely.

I remember plenty of railroad track embankments that were up for sale (railroads were exempt from abandonment/sales by law, but the slopes of the land on either side weren't and they always popped up - of course completely useless as an example). 

Did Canton GA (or Cherokee county) land a new auto manufacturing deal lately?