As an adult, is there any benefit to resealing my teeth as a preventive measure?

Possibly: There is a great device on the market called spectra. This system uses doppler like technology to detect cavities. Older systems like diagnodent are still valuable. Go to a dentist that works in microscopic loupes. This gives maximum visibility and with the other diagnostics available will give you the best results. Sealants can be great for kids. When the sealant is removed it must cavity free.

Limited Use: Sealing is misunderstood. It does not seal the whole tooth. It is designed to fill very narrow grooves on the tooth that a toothbrush cannot get into. Only a dentist can tell if currently have a groove of this type. Usually at your age, any exposed grooves have started a cavity and needs a composite filling. See your dentist for specific guidance.

Better ways: The best method to prevent cavities is proper brushing and flossing, avoiding foods and liquids that promote tooth decay, and seeing your dentist for routine checkups to monitor your oral hygiene and dental condition. Sealants do not provide a "protective shield" over the entire tooth, and can only be used for defective pits and fissures, and therefore have a limited use.

Yes, but very small: The teeth have grooves in them called pit and fissures, sealing them help prevent food from sticking into these tiny grooves.