Yes, these Weldon Champneys (or Champness) are a bit of an enigma are they not. And there are more. The first Weldon Champneys was born in 1736 and he was the grandfather of two of the subsequent Weldons. His mother's maiden name was Weldon so that is where the name came from. So I think there are three distinct people.
1. My Weldon Champneys, born 1803 who married Nancy Rawlins (1800-1828), had a daughter, Amelia Lavinia born 1824 and who seems to disappear from view after that. He was described as a clerk in 1823 on his marriage certificate and an attorney in 1847 on his daughter's marriage cert.
2. William Weldon Champneys, who was the famous clergyman and Dean of Lichfield (1807-1875) who was cousin to my Weldon (their fathers were half brothers)
3. Weldon Champness - don't know much about him. I think he was the person who married Sarah Taylor in 1829 because as you say, it states he was a bachelor so unlikely to be the same as my Weldon. There are later census entries when he is described as a caretaker or a chapel keeper so again unlikely to be mine as its a bit of a come down from an attorney! Surname spelling varies between Champneys and Champness. There is a death of a Weldon Champness in Shoreditch in 1886 which I am guessing is this one, and I have traced a christening of a Weldon Champness on 23/8/1807, born 22/7/1807 at Academy Chapel, Hoxton, London - parents William Champness and Mary. I do not know the back ground of William and Mary though and have not bothered to look further as its not my line.
Hope this helps!
Best,
Brett