Most visitors to Mesa Verde only visit the Chapin Mesa area, and if your time is short, that is an appropriate plan. Wetherill Mesa is a longer drive, and there are only a few sites to visit there, so it could be skipped if you're schedule is tight. But with a half-day or more to spare, Long House and the other sites on Wetherill Mesa are definitely worth the extra driving (and the drive, like the other main park road, is absolutely spectacular and provides great views).