Is intentional anti-gentrification a tort?

This is an interesting hypothetical. Depending on exactly what happens, you could be committing one of two torts, fraud or nuisance.

Fraud: If your stunt causes homeowners to panic and sell to you at a lower price because they fear the homeless are moving into their neighborhood, you have committed fraud. This is fraud because you have a) misrepresented the truth; b) the homeowner believed your misrepresentation; and, c) she was harmed by acting on your misrepresentation.

Nuisance: If, however, your stunt causes other buyers to panic, and make lower offers, you have committed the tort of nuisance. This is not fraud, since the homeowner did not lose because she believed your stunt, but because others believed your stunt. This is a nuisance because your stunt imposed real and substantial loses on the homeowner, with no off-setting legitimate benefits to you.

Note: You can commit nuisance, even if you do not personally profit from your stunt.

Interestingly, your scheme is almost the reverse of classic blockbusting of the 1950s and 1960s. Blockbusting real estate agents would get white homeowners to sell to them at low prices by telling them blacks were moving into the neighborhood. They would then turn around and sell the houses to blacks for higher prices.