It should update every 6 hours (or whatever CHECKINT is set to) even if wifi is off. The error it's generating shouldn't stop the script. It should continue on. It's just making noises to let you know something failed, but it should keep going.

As for the CPU, I don't know. I use QueenBee Widget to update mine, and that works well. I know others had issues with it because it was an old (pre PR1.3) version running on PR1.3. The script doesn't interact with hildon-home at all, though QBW and alarmd do I think. Either way, if it were the script causing the issue it would be eatting CPU, not either of those two.