(G) Turning a Marea Weekend 2.0 into a Focus ST170 Estate

I've just "discovered" the Marea Weekend 2.0 and am having an enormous amount of fun with it. Previously I had a 1.6 Focus Estate, which handled brilliantly and had great brakes, but was pretty gutless. Before I got the Marea I'd always wanted the ST170 estate version of the Focus, but never had the funds, and now realise I've (almost accidently) stumbled across something that's nearly as good as an ST170 (and looks better, especially from behind, IMHO)

My Marea is a W reg with 89,000 miles and is in good condition, with the cambelt having been done and a fairly complete service history. It was almost absurdly cheap and as a result I'm not averse to spending some money on it. I'm not interested in making it look flash and appreciate that the Focus is a brilliant handling car so it'll never be quite as good, but wondered whether there we some improvements I could make to the Marea that would bring it close?

Areas I'd like to improve include:

1) Handling. I'm guessing stiffer springs would help here. What sort of cost would I be looking at, and how involved is changing the springs? Also, would bigger alloys and hence lower profile tyres improve the handling? Again, what sort of cost would this be, and would I be able to sell my current (standard ELX) alloys?

2) Brakes. Whilst the brakes are powerful they lack feel compared to my old focus (which just had bog standard discs and drums, so I'd expect the all round discs on the Marea to be better). There's plenty of pad and the discs aren't scored, and various posts here seem to imply that Marea brakes are pretty good, could it just be that I need to flush the brake fluid? Otherwise, would better discs and pads improve feel?

3) Seats. The driver's seat is pretty saggy - I suspect a previous owner was quite large - but rather than replacing it with another standard Marea seat, could I fit some more sporty seats out of (I assume) a Bravo HGT?

4) Performance. The engine's already brilliant and I don't see the need to spend a lot of money here, although I'm considering putting a Green air filter in. Is this likely to improve the MPG? (although I think controlling my right foot will have the biggest impact here :-)

All ideas and suggestions welcomed!

1) Bigger alloys will improve the handling however expect to see a slight speedo misread, and obviously going too big will result in poor performance.
I would imagine you would seel your current ELX alloys, there is the classified section of the forum, or theres the free ads in the paper or even ebay them

3) You will find it hard to find a seat sold in singular form, but places to look are the scrapyard or ebay.

Get a K&N filter in there.
Gives you an extra 2-3mpg if you can keep your foot off the gass pedal
Makes a good engine great

Thanks for the advice. For the moment I'm getting a full service done at motormech in Birmingham next week, including a K&N filter. The more I drive it the more I get used to the handling and brakes and they're actually pretty good, so I won't go crazy there just yet, but will see if I can get a pair of seats from a scrap yard.