I actually went through the exact same agony, girl. I feel your pain too. *hug* I have Miranda in bordeaux, and I really wanted a whiskey Lily before they sold out. I ended up being lucky and returned 6 items I hadn't used before (two bags and 4 accessories), to raise most of the money for the bag. I just couldn't bring myself to part with Miranda even though I hadn't worn her yet.
A couple things I've noticed about Lily: Super heavy with my stuff in it. I'm not carrying too much like I normally do either, just hand lotion, wallet, sunglasses and case, mini skinny, keys, and a few other small things. Also, with my stuff in it, even though Lily is clasped on the middle turnlock, it loses that slouchyness in the top middle that I loved about it. It ends up looking square which isn't what I wanted.
The jury is still out on whether I will keep Lily, so I would definitely hang onto Miranda if you know you like her.