I got a replacement off ebay - an adhesive mirror that you stick on top of the existing one. Works a treat and you would not know the difference. Cost about a fiver (new) if I recall.
The first thing I'd upgrade would be the headlights. It's not until you drive a Corrado at night in the country that you realise how piss poor the originals are. You can buy a wiring loom and bulbs for about £40 on e-bay.