Bottom bracket is always a good upgrade, even if you cant show off about it. Shimano UN72, or the Tange equivelent (same factory, different label) is good, but make sure it fits your cranks. Royce is maybe a bit over the top.
A good handbuilt rear wheel is always better than a machine built one. You dont need to go with fancy components, an LX hub(what are they called these days?) with a Mavic rim and DT/Sapin spokes will do very nicely. Your old wheels are always useful as spares. You do need to get it done at a competant lightweight bike shop.
It pays to start with a good frame and adaquate components, then upgrades are really worthwhile.