The structure is OK. I would call the phrases adjective complements.
Are sentences '1' and '2' correct:
1) I do not think it is important, probably not even worthy of mention.
Meaning: I do not think it is important. It is probably not even worthy of mention.
2) I do not think it is outstanding, probably not even good.
Meaning: I do not think it is outstanding. It is probably not even good.
I can understand them, but grammatically speaking, they don't seem to make much sense.
How about changing the punctuation in 1)?
Thank you very much Mike and Tdol,
I am sorry Tdol. I just saw your reply now. The notification e-mail had been sent to my spam box.
How would you suggest that the punctuation in '1' be changed?
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Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.