In reply to JamButty:
If:
- you like the frame (stiff enough for racing, good size and shape for you)
- it's not industrially heavy
- you're not into hills as a big thing
Then new wheels would probably be a better spend, but look carefully at what you're spending your money on.
You could go value for money, say Pacenti Forza at <£400 ex tyres., or buy some really good hubs and get them built up. Chris King hubs and, say, DT Swiss alloy rims will set you back £1000 but the hubs will last forever if you look after them - put new rims on when needed.
Then some decent tyres for either option - Vittoria Corsa for me.
If the ride's a bit harsh, put some Enve bar tape on it (£40) and buy a new Fabric saddle and a carbon seat post. New wheels will make the ride a lot more comfortable than 'stiff' machine-made wheels
Total spend wheels £1000, saddle £50, tyres £100, seat post c. £100, bar tape £40. £200 in change....
For £1500 on a new bike, but you'll have a slightly lighter frame, and some new bits and shiny paint, but you'll probably have heavy wheels and it's unlikely to be all 105. So finish it all off with a bottle of car polish and give old faithful a real clean and polish