Guaranteed somewhere on that fence is the manufacturer's name and or the company that sold it to the original buyers. I would find their name, ask them what it cost for the material AND labor to put that fence in, and how many feet of fence it is total. I guarantee you the price of that entire fence will blow you away.
DO NOT ever think of painting it, period. And NEVER black. You will destroy what you have. Vinyl cannot go to black from white, PERIOD. I also guarantee it will warp and twist, and then you will have taken something with value and created a complete eyesore, and then you WILL have to remove it too.
Tell your wife to not let her personal taste interfere with your profit motive. The house/farm stable IS in horse country and that is where you need to market it. Check with local large stable owners, show them pictures, etc. I am certain they will agree to rip it out would be foolish. If you rip it where are you when someone who wants to use the property for horses asks or better yet says, "I'd buy it in a second if the pastures/paddocks were fenced?!'
Let the new buyer tear it out- you gain nothing and stand to loose greatly. Look past the fence!
I'd bet you have a $100K or more in fence there right now.
The people who can afford to install that much high end quality fence; the saying goes, if you have to ask, you can't afford it. Applies to Boats, horses, and high end 'farms' etc.