If a Patent has expired due to non-payment of fees and is almost 30 years old, can we apply for a similar patent (not a copy) as we have a similar idea.
It really depends on whether your similar idea has new, non-obvious idea as part of it. If so, you might be able to get patent coverage for the new and presumably improved part. What is covered by the expired patent is available to be used by anyone without licensing and your new patent wouldn't change that. You should, however, perform a search of similar patents since someone else may have patented your "similar" idea.
Patent idea needs to be unique isn't.