I only know one Imogen and her sisters are Natasha and Madeleine. All three beautiful names I think.
I do think of Imogen as being in the same category as Abigail. Along with:
Annabelle, Amelia, Amy, Anna, Alice, Alexandra, Bryony, Bethany, Charlotte, Catherine, Caitlyn, Chloe, Daisy, Emma, Emily, Eleanor, Florence, Felicity, Francesca, Grace, Hannah, Harriet, Isabel, Jessica, Jennifer, Joanna, Julia, Juliet, Katie, Lucy, Louisa, Melissa, Madeleine, Miranda, Matilda, Megan, Nicole, Natalie, Natasha, Naomi, Olivia, Philippa, Rebecca, Rachel, Rosie, Rhiannon, Sarah, Samantha, Sophie, Victoria, Zoe.
Names that have been consistently recognised/popular-ish for a long time.