You have two questions: Will you get in trouble if you make and sell a particular handle extender, and can you patent an improvement on an already known handle extenter.
The questions are not as tied together as you might think. As you noticed, US7032911 has gone abandoned for lack of paying maintance fees. A patentee can petition to have a patent revived by claiming the missed payment was either unintentional or unavoidable. Unavoidable is very hard to prove and unintentional does not fly at all after two years. This one is close to two years right now. As a patent no longer in force, this patent can't be used against you. But the thing you plan to make might very well infringe some other patent that is still in force.
Improvements to known things can be granted a patent if the improvement is new and non-obvious. What that amounts to is very specific to the details.