We're mostly aware of the focus on front weight. It's hard to find good savings up front through. I can tell you from my experience (I'm sure many others could too), your questions above:
- Most aftermarket strut bars are larger and stiffer than the original. Not sure what the weight diff is, but I'd assume heavier.
- Lightweight front 2pc rotors are awesome, if you're at a point where the money on them is justifiable (keep in mind it's not a one-time thing, you will have to replace rings).
- Yes, you can pull all the plastic crap out of the engine bay, it works fine. If you go the extra step of pulling the top edge stuff by the windshield you get some engine bay heat reduction to boot, but I wouldn't run like that on the street.
- Yes, Long-tube headers are a well-documented weight savings.
- Windshield (e.g. Lexan) is a bad idea on a car that ever drives on the street.
- AC - don't really know how much it all weighs, but I'm sure it's a good chunk on a car that doesn't need AC anymore.
Other front weight thoughts:
- Battery - one of the larger front static weight drops you can find. Downsize and/or relocate.
- Radio - The head unit isn't all that heavy, but combined with all the front wiring it's decent. Still, the audio hardware you'd pull from the center/rear of the car is considerably heavier, so in the net gutting all audio gear from the car doesn't shift weight in the good direction.
- Windshield washer reservoir (and associated tubing / jets). It's way out in the passenger front corner. You can get most of the savings by just keeping it dry instead of hauling a gallon of water out there. But the plastics are worth something too, and they also free up a good spot for running various cooler hoses or small cooler units. I've been running without one forever on the street, it's not bad. Just use gas station window washer squeegees more often.
- Windshield wipers - if you kill the wipers, motors, wiring, etc, it's a decent chunk and fairly high up. I wouldn't do it on a street car you might drive in the rain of course, Rain-X doesn't perfectly handle all conditions where you need to see out the front
- On the oil cooling front - probably one of the better options for decent cooling combined with weight savings in the right places is a Laminova oil:water cooling unit (inside the engine bay) and an upgraded radiator. Initial reports on this kind of setup from Travisjb indicate that the heat xfer works great, but you need additional airflow to the radiator to keep the water cool (airflow baffles in the bumper, etc). It's gotta beat running long heavy braided lines to a 34-row hanging way out on the front edge of the car.
As for top-to-bottom:
- Kill the XM Radio antenna from the top of the car if you have a touring model, plug the square hole with something (I just used a rubber plug and some silicone sealant).
- The headliner, auto-dim/homelink mirror, upper airbags, etc from the inside of the roof add up to a fair chunk up high. No point going down this route unless it's pretty much exclusive track machine though, in which case you'd obviously pull all the airbag and seatbelt hardware anyway.
- Z1's undertrays are heavier than stock, which is going to add front weight. But they're still worth it IMHO, and since the weight is so low they probably shift CG down by a hair. Ditto for extended/baffled oil pans - you want them for other benefits, but dropped CG is a decent compromise for the added front weight.
If you dig around the engine bay, there are a lot of smaller optimizations too. None of them are worth much individually, but over time every little bit helps. A recent example I found: in the driver's side front corner of the engine bay, you'll see a plastic fuse box attached to the wall with a couple of small bolts. It's marked on top like it contains several fuses and relays, but actually it's some generic part to several Nissan cars apparently. Open it up and there's only a single fuse or relay (I forget which) inside there, the rest is all empty. So I unbolted that box and got it and its mounting hardware out of the car, and just ziptied the one fuse/relay/whatever to the side of the nearby wiring harness it comes from.