ashley exhuasts are just generally piles of fucking wank only fit for the scrap heap. magnex, janspeed, etc seem to be the ones worth getting.
i think if youre happy with the car and just want it to go better then you should tune it, fuck saving up for a quicker car!

its very satisfying being able to take the car out after youve done something to it and feel an improvement even if its a very slight one. more interesting than being sat on the computer searching ebay and autotrader for the car you cant afford yet!
if it were me mate, id start collecting parts for a zetec conversion, get some uprated suspension and rs brakes or whatever on there, find someone local whose handy and willing to help out and itll be a proper little weapon when your finished!