Some have ferro fluid cooled tweeters, and that needs recharging. Rubber surrounds deteriorate, paper cones either get totally dry and crack or absorb environmental moisture and get mushy or even mold. Capacitors in the crossovers can fail, glue holding cabinets together may crumble, acoustic stuffing may settle or deteriorate. These are just the issues I've seen. Many speakers can be 50 years old and still work nearly as new.
Your LS50's have quality materials, expect long life and high performance.