Hi Darren,
I think thats one of those hard to answer questions as we all want different things from our cars. I have never been a spoiler, loud exhaust, after market wheels sort, preferring to enhance what is already there.
I went for Eibach springs at about £150 as i have used them on other cars, and they do the job without lowering it too much or destroying the ride. I will admit I dont work on my car as that isn't my thing, but they are straightforward as far as I am aware.
If you have more money then Tein or HKS coilovers would be the way to go, but thats over a grand and will change the comfort.
Sadly to do anything meaningful to the performance you are looking at serious money for forced induction as things like exhausts and filters wont make much difference for the outlay. But for me I bought the car for its reliability, the fact it is different (I have only ever seen 1 other car in my colour and wheel combination in 5 years) and that I think it looks absolutely great.
Once you have dropped it look at spacers as I love the way mine looks now and wish i had done that years ago. For about 200 quid you can fill the arches and improve the handling too.
good luck