Allegra - Ally is so overused - are there any other options?
I don't see any other nicknames besides Allie. Leggy and Eggy are definitely ones you'd want to avoid. Actually, I would avoid Allegra entirely as it is now firmly associated with the allergy medicine.
Calista - I could handle Callie/Cali, but would appreciate other suggestions.
Maybe Lisa? It's not really that long of a name that you'd *have* to have a nn.
Juliet - Jet is growing on me, but I don't love it yet. Julie/Jewel is a bit too dated. Lia is a bit of a stretch.
Juju? But it's very cutesy. Etta is gross. I only ever knew one Juliette, and she went by the full name.
Sapphira - I have no idea for this one!
Saffy?
Valentina - I hate Val, and Tina is too dated.
Vallie? Tina might be a bit dated, but so what? It's the most logical nn for a name that's fairly unusual.
Seraphina - Sera is too common.
Fina? Except it's a gas station.