You still get natural market appreciation over time and you can raise rents slowly, improve the property, and those things all increase the sale value (assuming the market is in a similar state).  

The only reason to stray from this would be if significant improvements are made to the property that affect the actual value. 

The areas that he/she will be improving are 1) revenue, 2) expenses, and 3) vacancy rates.

It’s also likely that the repairs amount will exceed the ARV.ARV: roughly $60-$70K Should I buy and hold this in hopes that the area improves? 

And once it is complete then do a refinance and use the proceeds to take out the original note and pay your improvement fund back.

It will eventually rent at the right price and as the weather improves. 

If you have a park that requires heavy lifting to fill spaces, sell homes, complete major capital improvements, etc, I would not recommend a 3rd party.

Is there an opportunity to raise rents at lease end or to improve the units at turnover in return for higher rent? 

I believe it improves the comfortability of the tenants who lives there.But it has to make Common Sense, Dollars Sense and Business Sense.  

@Joe Vahedi Every project I've done with recently added units has had some level of difficulty with appraisals - I have had to go out of my way to prove that the additional unit is permitted and compliant with zoning in order to qualify it with the underwriter and the income from it.Here's Fannie Mae's guidance on it: https://selling-guide.fanniemae.com/Selling-Guide/Origination-thru-Closing/Subpart-B4-Underwriting-Property/Chapter-B4-1-Appraisal-Requirements/Section-B4-1-3-Appraisal-Report-Assessment/1736875861/B4-1-3-05-Improvements-Section-of-the-Appraisal-Report-10-24-2016.htm#Accessory.20UnitsLenders and underwriters can speak to the details better than I can, but I would be VERY cautious about assuming a building with an unpermitted unit (even if typical for the neighborhood) would appraise with that unit included.