I would get omniums instead of messengers. They can be found for around the same price and are suppose to be the bees knees. People even compare them to sugino 75s.
I got a thomson seatpost off ebay for 70 new to replace my stock one, trust me its a worthwhile investment, they really are nice and pretty much 'perfect.'
If you have the money I would sell off the stock wheelset on CL for like $50 and use the money towards a new nice wheelset on bicycle wheel wareouse or something. Upgrading wheels makes a huge difference in ride quality.

Also you could make cheaper cosmetic changes, like switching out the stock stem for something more sexy.