Ooh the joys of your first car :-)
What about things like Colour coding any plastic bits?
Paint up your Calipers - nothing like Red but just a nice silver or something - anything that neatens it up or makes it look cleaner i think is always good.
Nice stereo system was always a must hehe
Just avoid things like Sun-strips, viper stripes, chrome stick on stuff in general......
Less is more ;-)
Maybe look out for 2nd hand bits on Ebay or things from Scrappy's such as a SRi Spoiler - if it's genuine Vauxhall parts i wouldn't consider that to be "chav" - not as if it's very big, just nice and subtle....
Most things will hurt on insurance but lowering with a nice set of Vauxhall rims (think of other models around the time, SRi, Vectra, Calibra etc would look nice but i guess that would cost too much to insure really....