Yes, it's worth doing if you want to get more enjoyment out of the car and aren't concerned with parting with some of your hard earned cash.
What would you most like to improve? Are you looking for straight line speed or some fun round the twisties?
Personally I would upgrade suspension first. Brakes are pretty decent on the 206cc (?! feel free to disagree) but I would be interested to know if they run a 266mm single piston caliper set-up or something a bit more meaty?
In terms of suspension, you are looking at some stiffer springs and sports shocks front and rear. In terms of 'lap times' this will give you the largest improvement. Upper and lower strut braces would also improive handling significantly. After that you are looking at more serious suspension mods such as poly bushes, group N or A engine mounts.. I'm not sure what size anti roll bar the 206cc runs as standard but a 25mm ARB might be an option.
If you are not interested in this side of things, then engine wise, go for breathing mods:
-Enclosed induction (air filter) without a resonator.
-Stainless exhaust system (manifold back, with the option of a sports cat or de-cat)
Make sure you don't scrimp on tyres! Get something a bit decent.