I wouldn't step one foot on that property. Any damage or suspected damage done will have the letter writer's fingerprints all over it.
Instead, I'd spend whatever money I planned to use to hire a lawyer and get a billboard in the area and post the address and when the parties usually occur. Then something related to "great time for swingers(1); owners don't mind if house is partied heavily in and trashed (2); might score some blow...(3)" crap like that. I'd use very vague vernacular. At the very least, there would be increased police patrols on the street.
Short term headaches? Sure but their party renters would dry up in a second and they'd either sell or rent it out to a respectable tenant. The sign comes down when a sales contract or lease is signed.
(1) You were under the impression there was a swingset in the back yard
(2) You have to take out the trash after a party
(3) Order a few Tootsie Roll pops and have them delivered to the address; keep the receipt
The other thing I might think about doing is, if I could grab a few old, cheap vehicles, park them in front of the house on party days.