Well... here's a few suggestions with yr £500
1. Sound deadening material for the doors
2. Carbon fibre for the aluminum dash to freshen it up
3. Replace the mesh wind deflector with a glass/perspex one
4. Some new BMW alloy valve caps
5. new centre alloy wheel caps if yours are getting a bit corroded
6. a strut brace accross the engine bay
7. one touch hood opening relay
8. set of new raybands just for the car
9. front PDC as I've almost manked mine twice
10...making sure to leave enough spare for a full tank of super unleaded fuel to rag into the atmosphere to really enjoy the company of your new purchases ...