Although you can't make a silk purse out of a sow's ear, you can make your older embroidery machines perform as good as they did when they were new.
You just have to make the determination if it is worth it or if you are better off getting new (or newer) equipment. I can assist you in making that evaluation.
Even without a major overhaul, there are a lot of small things you can do to improve your machine's production and profitability. Many of those things you will find on this website as it develops.
I am available for embroidery consultation from hooping techniques to employee management.