Personally I would have held out for at least a facelift 1.6. How come you went for a 1.4 out of interest?
Saying that, i've done a few bits and pieces to mine (1.6) but everything that i've done i've got for next to nothing/eBay bargains etc. I certainly wouldn't have spent big money on it!
Here's what i've done, which might give you a few ideas:
Colour coded bumper inserts, side strips and door handles
17" OZ Superturismos
30mm Eibach springs
K&N panel filter
ST170 snorkle
ST170 airbox
2.0 auto air deflector
ST170 lower grill
LHD reverse light
US spec rear lights
Smooth rear wiper
Stainless steel exhaust tip (wasn't bothered about extra noise etc so didn't want to fork out for a backbox)
Like I said everything i've picked up has been dirt cheap so it's not cost much at all, and imo it's a pretty smart first car.
How it stands at the moment:
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http://i362.photobucket.com/albums/oo61/robmather88/sun1.jpg[/img]
Edit: I found quite a bit of difference with the ST170 snorkle/airbox, the auto air deflector and the K&N panel combined. Quite a bit more "revvy" and a bit more "go" especially lower down in the rev range. Doubt it'd do anything on it's own although they're only a tenner or so from Ford so it might be worth a go?