In these days of cheap disk space, freely available filtering languages like our beloved Perl, and fast editors with good search commands, selective logging of warnings and errors is almost certainly the wrong choice. Remember, you can always filter downstream, but if valuable information is ignored, you will never get it back.
That's a good point. Big logs are much less of a problem that in bygone days.
Still, if you go this way, be sure to do a back-of-the-envelope calculation to guestimate how much disk space your logs will grow per day. You'll also want to have some sort of log aging scheme. Having a system roll over in the field because the disk filled up can be embarrassing, especially when everyone claims it can't happen.