What owners manual or service manual are you using???? Even most motorcycles now have 30k mile valve adjustment intervals. Newer Accords have a 115k interval. Older cars are 30-60k.

Valves simply don't go out of tolerance that quickly anymore.

Springs do soften over time, but on a stock engine with a 6500 RPM redline.. i don;t expect valve float from too soft springs ot be an issue. I don;t hink it would be nessesary until you replace the piston rings during a full rebuild at 200k - 300k miles when they wear out.