do you have any pics? your quill stem was the current style back them as threadless headsets and stems were just coming onto the market and were still mostly a MTB thing.
5000 miles is alot on what is likely a Dura Ace drive train yes? have you been repplacein your chain frequently? I would say you should be on your 4th by not. if you haven't been your first upgrades (or repairs) should be chain, cassette, chain wheels.
depending what you do with the bike most people will agree a good set of wheels is a good starting place for an upgrade. depending on your current wheels and again what you do with the bike you can shave a few pounds and get better performance. changing the wheels would also be a stasrting point to upgrade your drivetrain to 10spd. you can buy new wheels and run 8spd then upgrade your shifters later and buy the new cassette then too.
odda are that while a new carbon fork will look good it will change the ride you are comfortable with. it may seem stiffer or harsher as the carbon fork may not dampen road shock like your Alloy fork.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk