Thought i'd add my 5 cents worth in no particular order or preference...
- Stripping out the interior is a no-brainer - i'd estimate that you'd shave 60-80kg from it's kerb mass.
- Possibly replacing the glass windows with lexan or an equivalent material that's lightweight but economical (if available).
- Relocating battery to the boot for better weight distribution.
- Good tyres are a must have if the budget can stretch, i'd go for semis. Price-wise, they are ridiculous for 17" and above. Toyo R888's are cheaper than Advans or RE55's... i'd predict $300 a corner for R888's to suit a 15" rim.
- Slightly lowered suspension (1 1/2" all round) with good quality adjustable shocks. Lowering too much can have adverse affects on handling.
- Add a strut brace and swaybars to the equation.
- Brakes are very important as braking zones is where most overtaking moves are made. I'd step it up in this department and go for VR-4 calipers with good quality slotted rotors, pads and brake fluid.
- Replacing the radiator with an alloy unit will save around 10kgs.
- Removal of A/C will produce a saving of about 30kgs.
- A half decent intercooler... i'd go for a Jap-spec VR-4 before an RX-7 series IV unit to reduce heat soak. They're one of the best barring an EVO or GT-R item.
- Definitely an oil cooler if you don't already have one (preferably upgraded) and maybe a transmission cooler if gearboxes become a weak point.
- Some form of LSD is a must. I can guarantee you that from experience. I am not sure about a welded diff though - I can imagine it to be a pig to drive.
- Roll cage (even if it's a half cage). It may add weight but the increased rigidity you'll notice and of course added safety gives peace of mind.
I don't think you'd be wasting your time with FWD... if so, I wouldn't have wasted so much time and money on mine. Many FWD Hondas are reknown to be real 'movers and shakers' around a racetrack by keeping up with much more powerful machines. In saying that, there's no reason why you couldn't do the same with a well sorted cordia.
Hope I have added some useful info. Good Luck!