I'm the Australian connection - somewhere, I'm sure of it!
Have seen similar information regards Theophilus & Elizabeth Plenty in Family Search, so the other info about his son Charles Plenty's family is handy.
My side of the Plenty family moved to Australia in 1858.That was Charles Plenty (b1824) who had married Kezia Parfitt (b1818) in 1850 at Abersychan in Wales.I believe Charles and 4 brothers moved to Wales in the early 1800s for work in the Tin mines from Somerset.So far no link has come up, although I think one of the brothers names was William and another was killed in a mining accident in Wales.When Charles Plenty left Britain for South Australia he had three children, Fornham, Calib and Tryphena.
I can't confirm but we think that Charles' fathers name was John Plenty who had married an Elizabeth Dowling in 1823. So far have not been able to confirm that link - does this ring any bells???
Do you have any information regards Theophilus' parents???