It has been established that some people prefer copper over aluminum. I myself really don't care... As it has been stated already, the smaller size branch circuits need to be copper. Failure at devices is common and fires result in many cases from the arcing.
This is the last opportunity to answer the original question.
Can Vreelander safely replace his 50 amp breaker with a 60 amp breaker?
Considering it is aluminum wire and it is #6, will this be safe?
I say go for it. Make sure the new breaker is al/cu compatible.
The label on the back of Bethany's range, specifying copper..
well, I'm sure they're talking about the cord. Aluminum is not a good material to make a cord. The cord needs to be copper, it will last much longer.