To restore the shine, apply two coats of wipe-on polyurethane (available in gloss, semigloss and satin). Wiping results in a very thin, fast-drying coat, so flaws like dust nubs or sags are less ...

Polyurethane is probably the best bet, for constant color and the least amount of wear. It can be applied in almost any fashion (spray, brush, etc.), but for handrails I like the wipe-on method ...