I've not fishing that rod, but my understanding is that power to play bigger fish and reach are the main limits, perhaps casting into the wind as well.
All the streams I've mentioned are darn small, and I can't see the shorter rod being a major limitation. Your chances of catching a fish bigger than 12-14" is also very slim.
On the other hand, they're open enough to use an Amago (I've done it), so if you really "need" another rod than this would be a good excuse. Then you'd be able to use the bigger rod on the lower Firehole, upper Madison, and Gibbon.
I use my Amago for everything these days. Nice when you randomly catch a big fish in a tiny little steep stream. The other weekend I was glad I had the big rod, endless overhead snags nonwithstanding, when I hooked a 16" bull trout and it took off downstream into a series of 2' boulder cascades.