Maybe we've got the trope from the wrong perspective. Maybe the real trope is "characterizing the attractiveness/sexuality of the character in a reserved or wholesome manner", and a sweater is just one of many techniques for doing so. Get un-hung-up on the sweater altogether.
The is definitely a trope, as Pleasantville calls it out explicitly. As with Wet Sari Scene, this a deliberate fanservice trope that consists of 1) a girl, and 2) a sweater. I think you can simply cull examples that don't seem to fit this or are disturbingly pervy. An example of why this is a useful trope would be in describing the subtle evolution of Velma from Scooby-Doo from gonk hipster to cute nerd girl.
On the merge proposal: Seemingly Wholesome '50s Girl requires the character to have a double life (i.e wholesome on the outside but actually not so wholesome), so unless this (=Sweater Girl) also requires that a merge is out of question.
Yeah, I overlooked the 'seemingly'. Rats. Wholesome Girl would be the supertrope. Adding the "Attractive" adjective gets us into the dreaded and despised subjective territory.
Not sure how many different ways there are to establish a female character as wholesome-ish. There must be more than just the one trick of stuffing them into a fuzzy sweater.
Because people assume they're separate options, despite what the crowner description says. They assume "rename" is one solution, and "redefine" is another, and they prefer the latter, as they should.
After we redefine, let's start a crowner for the new page's name. Normally, we need a crowner to decide to rename, but in this case, we're making a whole new trope. "Sweater Girl" can be one option on the new crowner.
As I stated above, and I will elaborate now, I believe this trope consisted of 1) a girl, 2) a sweater, 3) a non-explicit sexual appeal, especially of the boobs and figure. Connotations suggest "hotness" but also at least some adherence to mainstream standards of modesty.