Last night I converted about 300 groups into 1 component in 1 swell foop. It also showed I had about a dozen almost identical groups with a common very minor change in them, that did not convert, as expected, but they would be hard to find otherwise.
I did this by selecting ALL, and converting. After the conversion to a single comp, only those unique groups that did not convert remained highlighted. Note: it is not necessary to highlight any of the multiple groups, except the single any one group to effect the conversion. All same groups in the model will convert. I have not tried testing with layered and visible same groups yet, but I will.
Now I will try to figure how to convert those similar groups into the same single comp. I think I know how, but I haven't figured out the correct sequence yet.
(edit added) I just noticed that my old 43mb+ file is down to 31mb, and I'm not done converting yet. And it saves faster too. Bonus.