scotlass has mentioned some places we enjoyed also - Minack Theater, St. Michael's Mount and Lizard's End, where we stumbled upon a fun folk night at that restaurant.
Some other activities we enjoyed in Cornwall were the Obby Os festival in Padstow, as we happened to be there on May Day:
http://www.wikipedia.org/wiki/'Obby_'Oss_festival (edited to add, my link isn't working for some reason, but you can google for info)
We went on several countryside treks to ancient stone formations aka "quoits" ...
http://www.cornwalls.co.uk/history/ancient/stones.htm
(there's a really good stone circle in Lake District as well)...
and a beach with dinosaur egg rocks, Porth Nanven:
http://www.cornwallinfocus.co.uk/walking/w32.php?print
We did use flybe air, and learned why the locals call it "fly-maybe"
BUT I was still thinking that with your love of Sanibel, Lake District seems a closer match, largely for the lack of commercial development. Even the old stone fences have to be maintained according to code, which is why the sheep are usually seen wandering on the roads...
BTW windmillhill, Langdale area was about my favorite timeshare locale in Lake District, but it almost never comes up for exchange in RCI - I envy you!