I feel Magnolia is the name to use - it has so much symbolic meaning for you, it gives Maggie, Lolly, Nellie, Nola, Lia; and it’s never going to be a “six kids in class with the same name” name. If anything, the trends are moving (slowly) to mid century names.
Hope comes across OK over the internet, but I am not super keen on any of your middle names. To me, Magnolia & Vivienne compete, not complement; I don’t love how the A of Magnolia runs into A of Adeline and visually that they have so many repeat letters; and I like Claire but don’t see it as the Frenchy-French name - it’s of course very French but I mean, it seems more Irish to me. If had to choose would go Claire, then Adeline. Actually, Magnolia Claire is very pretty & delightful!
If you’re not sure, perhaps consider: Magnolia Lucette; Magnolia Cosette; Magnolia Delphine; Magnolia Marie-Claire; Magnolia Sabine; Magnolia Sylvie; Magnolia Zélie; Magnolia Frances; Magnolia Faye.
Either way, I don’t think you should let worries on popularity hold you back from this name. I’m not sure it’s as much like that these days, especially for girls’ names.
What’s more likely to feel trendy (as @tori101 reminded me of) is the sound: we are just heading out of peak E names and L sounds in girls’ names. So you may still get several Ellies, Eloises, Lilys, Milas, Laylas, and Matildas in your daughter’s class. The nn Valley (if you go Valencia) will fit into that trend. It won’t escape!
That said, and turning more fully to it, Valencia Rossi is a super swish name - as in a showstopper. If these names reflect and speak to your heritage, then maybe that is a good switch? How would you feel about giving up Magnolia?
Rather than popularity (as neither popular and / but both trendy in a certain L way), think you need to decide if you want something “Southern”, sweet and charming, or “international”, assertive and glam.
Hope this helps! 