Your travel buddy will have plenty of opportunities to do that in Vegas, Zion is definitely worth the detour. I visited while I lived in Vegas and was very impressed with the park. I wouldn’t put it in the same category as the Grand Canyon, but it is certainly one of the most amazing National Parks I’ve visited. A drive-through would be an injustice. Zion has great hikes. My personal philosophy when offered the possibility to go to a National Park is always to go, you never know when you’ll have the chance to go again.