I haven't been very active on these forums lately, but I thought I'd check in with my sway bar experience over the last two autoX seasons.
I removed my rear sway bar at the end of last season. With a rear bar (I used the "comfort" cobalt sway bar) the car was tail happy and unpredictable. I could not get the rear to stay planted, even with the rear dampers super-soft and the front cranked up hard. I did not alter spring rates, just the damping rates. Even with a staggered tire fitment (255 rear, 225 front) the rear would step out on corner entry under braking, mid corner, and under power. It was a handful. At AutoX speeds below 60 mph this is fun, but at race track speeds of 100+ it's terrifying.
I removed the sway bar for the last couple autoX events last year, and it was much better. Body roll is still minimal simply because the car is so low and light. It's now very nuetral, though lift-off snap oversteer is still a thing with any mid engine car. It's no longer treacherous to drive, and I've been able to increase damping rates on the rear to better control things back there without it stepping out of line constantly.
Bottom line, if you're going to do a sway bar at all, I think you do the front one first. Doing just the one in the rear is playing with fire. I think most people will be happiest leaving it well enough alone, and balancing things with spring/damping adjustments.