I just put a cusco one-way in the front of my R34 V-Spec (<$1k landed). A-LSD hasn't caused any issues as yet, but I've not pushed it hard or been on the track yet.
The A-LSD thing is annoying. If it was as easy as replacing the centre, I would have done it already given everyone's feedback on diffs.
I'm doing similar things to the OP:
Got Bilstein PSS9s, Ikeya upper arms F+R, DBA4000s, crap pads (going to change) and have ordered the Whiteline sway kit F+R+links.
Having said all that, you can't discount the impact of good tyres. I'm running on 400 treadwear P-Zero All Seasons which are not confidence inspiring at all. Would budget for good tyres.
Feedback on rigid collars is interesting.