I wouldn't get anything new by upgrading to FF2, I've got 45 extensions which do more and better things than FF2 in better ways. You can always use SpellBound for FF1.5 for spell checking. I'm using it now.
If I upgraded to FF2, I would only be able to do less things, as about a third of my extensions don't work with FF2. So the only reason for me to upgrade, is for security issues...