Yes I've read the book and seen the lovely film with Daniel Day Lewis, Helena Bonham Carter and Julian Sands (not to leave out all the other wonderful actors in this version.) It's one of my most favorite books.
You ask what does Lucy see in Cecil? Not much, really, except a guaranteed successful future with an established aristocratic family and therefore a secure future for a woman in that day and age. Cecil is the man Lucy
should want for a husband. Lucy tries with Cecil, she really does but there is nothing underneath his veneer. Cecil is a prig and a bore but she tries to let that go for the sake of what is expected of her. She knows in her heart he is not the right man for her but she feels she has no choice. Her family's future is uncertain, the Honeychurches are not of the upper classes nor do they have the background bred for high society but Cecil feels Lucy can be molded into what he wants. Lucy's mother is very much for the match. She, no doubt, had no choice either as to whom she married and sees in Cecil a grand opportunity to secure Lucy's future.
I was surprised at first when Lucy returns from Italy to announce her intent to marry Cecil. She sees no hope or future with the bohemian George, it's against all she's been taught. She must stand by her family and society's principles that she marry well.
---But how can she go against her heart-? (...I ranted when I first read the book--ha) But matters to do with the heart or with love mattered little in this Edwardian day and age. It was a matter of security and doing what society deemed best for young women. It took a lot of guts on Lucy's part to break off the engagement with Cecil; but after having a talk with George who tells her of Cecil's true nature about women, she decides she cannot go through with it and this is
before knowing George will be there for her if she does so. Can anyone blame her for choosing George? No way!
