I would just clean it. I don't see any reason for an accumulation of grease & dirt just because some previous owner neglected to keep the car clean.
I also don't understand people who leave worn-out parts like plug wires on an engine that needs them replaced to run properly; clean & bag the originals, put on the most accurate/correct replacements you can find, and respect the car. Same for leaking gaskets, dry-rotted tires, shredded upholstery and rust-through.