It is Selden's self that Lily is attracted to; she likes his ideas and his personality, and it is only with him that she acts like herself, but his status is not exactly desirable; although he is accepted into New York society, he is not rich.
On the other hand, Rosedale's status is certainly appealing to her - his monetary status, that is, not his social status - but she cannot accept him as himself; he is small and plump and shiny, and she is disgusted by his attempts to infiltrate their exclusive "set". For her, as well, his religion and race were detractors - anti-Semetism was not unusual at the time.
Throughout the book so far, Lily's trouble with finding herself a husband - and that is her greatest concern, for the most part - lies with her inability to reconcile self with status. She tells herself that she wants - no, needs a rich husband; an effect of her upbringing and peers: gold digging is not only applauded, it is expected of her. However, although she manages to position herself to get a rich husband more than once, she finds the man himself unsuitable and sabotages it. Yet she is unwilling to consider marrying a man she loves, but who is not rich.
The lost conquests we see in the book are (1) the Italian prince, who is rich and well-placed in society but who, we can assume, is old and not particularly handsome as Lily finds his young, handsome stepson better company; (2) Herbert Melson, who had "blue eyes and hair with a wave in it" and little else to commend him (beside being rich), and Lily congratulates herself in having dodged a bullet with him as he had grown fat and boring after marriage; (3) Percy Gryce, who is very rich and very, very dull; (4) Simon Rosedale, who is very rich, very disdained by society, and (gasp!) a Jew; and finally (5) Lawrence Seldon, who is handsome, kind, a bit idealistic, and not rich.
One of the biggest selling points of romance is the idea of an "unsuitable" or generally unremarkable young woman who finds herself a charming and rich young man to fall in love with and live happily ever after with. As we know, that rarely happens, but it is what Lily is hoping for. Sadly, I doubt that this book is going to be that kind of romance, and I doubt that Seldon will suddenly come into a fortune and marry Lily. This isn't Jane Austen.
It'd be nice, though.