Why is my agave "blue flame" sad?

My blue flame agave isn't doing that well, I'm afraid.  There appear to be two issues.  

1. Large-ish brown spots appear on random leaves, often at the base.  I suppose that overwatering could be the source of this, but I don't really water it it very often, the spots aren't especially mushy, and there are no other signs of rot.
2. Unhealthy-looking yellow dots now adorn many of the leaves.  You can see a close-up in the last picture below.

Does anyone have any idea what might be going on with my blue flame?  I'd welcome any advice...