100% correct about two spares, unless you are running 8-ply BFG's or the like. I've broken two tires at Steens. The gravel they use on the roads is really hard on typical street tires. The road is also typically very washboarded; in my truck I just go fast enough to float on the ripples and it's like driving on packed snow basically. Some vehicles you can't really do that and it can get tedious. RV's, big vans, short-wheelbase SUV's, etc. Just FYI.
If you PM me I can describe a short hike at the top-ish of the mountain that'll blow your mind. Failing that the hike to view Wildhorse Lake is worth it.
Steens is a sublime place.