Thanks again to all for the input. Richard, you are exact with your analysis and I understand that in the future my attitudes towards bikes may change, but for now a "comfort bike" is the best route get into "born-again" cycling.
Cycling is indeed more comfortable the more they do it, I am now averaging 15 miles a day on the old Schwinn, wishing for a low gear so I would not have to stand up and pump going uphill, and a high gear so I could go faster without pedaling out on the flats. BTW, the "gear inches" on the Schwinn is 61, which is equivalent to 6th or 7th gear on the middle chainring of the bike I rented.
After riding my brother's Trek 7000 mountain bike (with clip in pedals), which I found efficient but immediately uncomfortable, I've decided to buy a Jamis Explorer 2.0. Many bikes are in this category, but I wish to patronize my LBS, which hopefully will have this bike in stock soon. The Explorer 3.0 exceeds my budget, plus I need funds for accessories.
Converting the Schwinn into a 3 speed or 5 speed is on the list of desired toys and projects.
Now it's off to fix the latest loud noise that developed on today's ride with the Panther. Probably should have not ridden it across all those ruts in the field..........