Ah, I forgot to post a follow up to me re-tightening my bolts.
Firstly, the alignment doesn't seem any different. The left tyre still scrubs on the plastic inner guard same as before (I'm gonna take it out this weekend). The car steers the same (very nicely indeed).
However, when I went to loosen and re-tighten the bolts on the suspension arm, they felt kinda loose. Much looser than I remember doing them up, despite the rather "tight" thread. The main pivot bolt seemed as tight as ever though.
I can only deduce that when the car is on the ground, a lot of tension in the arm gets taken out and the 2 nuts at the suspension arm end aren't as tight anymore. This would also explain why it was virtually farkin impossible to get the nuts off the first time with the car on axle stands and wheels in the air.
So my advice for anyone doing radius rods - loosen the 2 nuts while the car is on the ground first, if you can. And after you're finished, tighten them up again when the car is back on the ground.