Hi LyndyNZ, we're also in our 60s, ex-Tasmanians.
Have studied your draft, here are some suggestions.
In Hobart, go to the Mt Nelson lookout (depending on weather) for a superb view of Southern Tas. Better than Mt Wellington.
Salamanca Market is excellent. In the remaining half-day you can do a circuit down "The Channel" via Snug and Woodbridge, into the Huon Valley via Cygnet and Huonville. There are other options but you can take your time on this circuit and be back for dinner.
Hobart to Strahan is 5 hours +. If time is pressing, skip Lake St Clair.
At Strahan, consider the ABT railway. www.puretasmania.com.au/default.asp?pID=46 This is perhaps the best railway & scenery trip in Oz. Take the bus back from Queenstown.
Our experience is that the Gordon R cruise is 80% about Macquarie Harbour and Sarah Island. Pleasant but you'd need to be interested in Tas history and convicts.
Strongly recommend that you drive from Strahan to Stanley (not Launceston) via Cradle Mountain. Stanley is unique. Have a crayfish at Julie and Patrick's. You won't see much at Cradle Mountain unless you stay overnight.
From Stanley you can ramble out to Smithton and drive back to Launceston - stop at Table Cape (Wynyard) for the view.
If you like wines, consider a wine tour from Launceston.
Re your days 10 and 11 - suggest you stop at Bicheno so that you get maximum time at Freycinet. You'll have to walk a bit to appreciate Freycinet. If you guys are fit (like most Kiwis) walk to Wineglass Bay, 3 - 4 hours return (if weather is OK).
You can drive to Port Arthur via Rheban and Kellevie - dirt road but quite reasonable. Saves a lot of time. Or you can enjoy the Prosser R valley and then tur off to Port Arthur via Buckland - Nugent - Kellevie. One full day is ample for Port Arthur and surroundings so you can gain a day. Port Arthur to airport is an hour.
If you want something off the beaten track, use the extra day to take a trip to Maria Island (ferry leaves Louisville near Triabunna). There are quite a few short walks from the ferry terminal of varying difficulty. You'd have to take your own lunch etc.
Hope all this helps - if you want more info, send me a Tripadvisor message.