No I look at both, I sometimes do pre-market trades but not nearly as often as regular market trades. I'll sometimes do after hours trades on earnings days.
Lately though, at least with AMZN, the pre-market hasn't had anything to do with the later action...typically, I get what you're saying, the pre-market high is re-hit later during regular trading, but lately AMZN goes up and then just drops. Ironically, now is not a bad time to be shorting but the shorts will get their shorts handed to them soon enough.