yes Crystal does the rev counter bounce when cruising from time to time, first noticed it at about 1000ks and she did it last night with 27500ks so she's not growing out of it. No driveability problem, although I find there is a slightly dead spot in the petrols between about 3500-4000rpm which I put down to the variable valve timing changing phase - once you get through the funny spot it'll pull like a demon all the way to the limiter. Every petrol i30 I've driven has that weird spot.
If you're getting a rev counter bounce and an actual loss of power concurrently then I would suspect that yes there is some sort of electrical problem. If memory serves me right the i30 will not drive without a cluster fitted so if that is the case it could well be a CAN-BUS problem between the cluster and ECU causing the ECU to not see the cluster and start faulting.
I connected mine to the GDS after the first time I noticed the tacho bounce but there were no fault codes. If the problem is reasonably widespread I'm sure they'll come up with a fix - they're pretty smart.