We've replaced the steel/rope Genoa halyard with a good quality Gleistein polyester halyard (no wire), braided cover over straight filament. This works well in practice and I don't think there'd be much benefit from going Dyneema here. You must inspect the masthead sheave for damage from the wire, but ours was fine. Replace if damaged or too rough - you basically don't want it chewing up the new rope.
Also don't forget to service your clutches while you're at it.
The main halyard is still original, although due for replacement soon. I think here (with our in-mast furling) there would be some benefit from Dyneema and I'll probably go for polyester braid with UHMWPE core. Gotta keep the size or the clutches won't hold it. Although the Gleistein type would probably be okay too.
