I have a 32GB Nexus 7, I've had no lag issues, no Wi-Fi or Bluetooth issues since the update.
When Google announced the 4.2 they dubbed it a maintenance update despite the new features 4.2 includes. The new features include, Multi user, Quick settings, gesture keyboard (swipe), Daydream, Lockscreen widgets etc. The whole OS with 4.2 is in my opinion is faster, smoother and generally an even better user experience than it was with 4.1.x.
I would encourage anybody to update their Nexus device to 4.2, I use most of the new features everyday and don't regret updating my Nexus 7.
If you really don't think you'll use the new features, it's your device, don't update it but you having a cutting edge device which if you don't update it won't be as cutting edge as it could be...