Just like you went through an underwriting process when you purchased the condo, the new buyer will have to undergo a similar process to make sure they qualify for the financing, even though they are assuming the loan.  

But I also don't want to renovate beyond what I can recoup in increased rent rates in an area that is still undergoing gentrification.

Gentrification:  the buying and renovation of houses and stores in deteriorated urban neighborhoods by upper- or middle-income families or individuals, thus improving property values but often displacing low-income families and small businesses.A large percentage of the city of New Orleans LA is currently undergoing the above process.

Does empty land price undergoes boom and bust like property ?

The refi is assumable but undergoes the same process as a typical loan, so not really seeing any advantage for the buyer.  

In a JTWROS the deceased owner’s share automatically vests by operation of law in the surviving joint owner – regardless of what the deceased owner’s will or other estate planning documents say.However, you may need to clear up the inheritance tax or there may be other issues that require you to undergo other legal proceedings in order to place the property in the survivor's name.

He now has two properties with tenants and a third undergoing (major) renovation.

A nice new construction single family rental in an A class area with A class tenants may be the 40% rule.Remember, the 50% rule assumes LONG TERM -- potentially 30 years or more...So, that older Class C will eventually have to undergo a big rehab and the expense ratio will drop. 

Additionally Central Heights is undergoing a bit of a renaissance as they build new restaurants, bars, shops, etc near heights blvd.

As is much of the US right now, Southern Vermont is undergoing some extreme weather right now.