hi,
1/ signalling : normally, only RA or LA update. If the core network is independant between 2G and 3G (can it happen??), I would also expect ATTACH/DETACH and PDP CONTEXT ACT.
2/ Ping-pongs with reselection… well, you can count how many LAU and RAU occurs. What you can do is play around with the parameters, in order to block the 2G 3G reselection, and then reactivate it. You should see the difference.
Regards
pix