I always try to have multiple tags. I'm usually targeting elk, but try and pick up deer and/or bear. In the big picture adding a 400$ deer tag or 100$ bear tag is worth it to me.
When I hunted MT we had both, and I saw both.
The year before last in CO I had elk, deer and bear tags, plus the family had some other tags. In 18 days, we got 2 elk, 2 deer, and missed a bear. I started opening morning(archery) with intent of finding mule deer, ended up with a bull on the ground before 9am. While trying to get my buddy on an elk, I spotted a bear, got within 50yds and shot right over his back. Got my daughter on a bull the second day of muzzy, then helped my fil get a muzzy buck. Then while trying to get my wife on a muzzy bull, I came across a nice Muley and got him with the bow. We also hunted the same unit two other years with only a missed bull. You just never know, sometimes it works out.
I would say focus on the species you really want, but might as well take advantage any opportunity that presents itself and have a tag in your pocket. Some would say don't bother with the other species, but if you're only out west for 10 days its nice to have some options.
If I remember right the bear tag isn't very expensive in MT and you can get otc. It could always be a backup if you go with one tag and tag out early