Purpose of the leap was to make sure Tess married, just in the twist it was Wayne instead of Doc. In early episodes, the leap objective wasn't always clear-cut or understood early on. I felt the same way you did about Double Identity
I don't think that's true, Tess married the person writing her love letters in the original history anyway...
Also, to quote Honeymoon Express - "JUST to help Buddy Holly with the lyrics to Peggy Sue?"