coralreef - if you're still reading --
I have recently decided that the John Hoare of the two bastardy bonds is my greatx4 grandfather. Lucky me.

He is not the John Hoare who was the father of Elizabeth Hoar borne 1766 / who married John Merrifield.
I have collected a load of info about him from the OPC site and elsewhere. His two actual wives (after his relationship with Elizabeth Harris) were Catherine Harpur and Maria Hugh(e)s. He married Catherine Harpur at St Enoder in 1783; she drowned in 1798 in Lamorran, and he married Maria Hughes in 1803. He had numerous children with Catherine in St Erme and Lamorran, and numerous more with Maria, who was some 25 years younger than him and had had one child before her marriage to John Hoare. He was resident in Newlyn when he married Maria Hughes (who was from Lamorran) and his last child was born in St Columb Minor in 1820.
I imagine he was the John Buncombe Hoare (the name is more commonly Bunkum) born in St Enoder in 1753, son of Francis and Hannah. (He shows in several online family trees as born in 1854). Their other children who show at the OPC site are Francis 1758 St Enoder and Ann 1760 St Enoder. (My woman, who seems to be an unrecorded daughter of John Hoare with one of his wives or someone else, named her first child Francis.)
So the bastardy bonds were at the beginning of his career -- they were in the two years before his first marriage, to Catherine Harpur.
For him (baptised in 1753) to be the father of Elizabeth Hoar born 1766, he would have had to be somewhat older, unless he began his career very early indeed. He was likely buried at St Columb Minor in 1828 at age 74. (Although if baptised in May 1753 he would have been 75 in October 1828, the rest of the details of his life make it pretty certain these were his baptism and burial.)
The Elizabeth Hore who was baptised in 1766 in St Austell was the daughter of John and Dorothy. There was also an Elizabeth Hore baptised there in 1767, daughter of Benjamin and Joan. And an Elizth Hore baptised at St Mary Truro in 1766, daughter of Wm and Jane. (All at the OPC site.) Was there an Elizabeth Hoar baptised in St Clement?
But ... I'm afraid I am lost -- someone born 1766 didn't marry 1762.
John Merrifield married Elizabeth Hoar in 1789 in St Roche. ("The Register records the groom's surname as Merrifield, but he signed Merifield") Is this your couple? (Oops, sorry, I just realized you must have meant John Merrifield was born in 1762.)
Anyway, I wanted to put the record straight on John Hoare of the multiple liaisons, and also wonder whether you know anything else of your Elizabeth Hoar's family. I'm looking for Hoar(e)s (or Hores) from that area who might be interested in doing DNA testing to help out with a puzzle I and someone I have just met have run into. Elizabeth's descendants wouldn't count, as we need YDNA from a straight line of men with the surname. If you know of anyone, I'd love to hear!