Verbal | The clothes looked more appealing inside the store than on the racks..

The sentence is fine the way it is. You are comparing 2 locations: inside and on the racks outside. The parallelism is regarding 2 locations. Furthermore, "on the racks" is modifies "outside" so you are comparing inside and outside.

"..inside the store than outside the store on the racks" is fine as well, but there's no such thing as "direct parallelism" that you speak of. You can omit some words in parallelism if there's no ambiguity. For instance you can
...

---