I really find it hard to let go of a doll once I have it. I have occasionally sold them, usually the fashion dolls. The only bjd I have sold was the one I bought because I couldn't get the one that I fell in love with. And then I could. I still miss Kaguya, but she went to a good home where she gets more love and isn't ignored, and Shirahime is here now and very happy. Strangely enough, I had been trying to downsize the herd. It's useless - I just received a new one today! I really hate ignoring Hazel, and she gets to go out most often. The others all get time too, although not as much.
Changing wigs, eyes and faceup can totally change the doll in question! Sometimes that is all it takes. Sometimes it is just finding a "hook" into the personality. One is a tomboy, one isn't, one is a Star Trek geek, one decided he needed purple hair. Another changed his name on me! Don't worry if that doesn't work, try putting the doll away for a while and thinking about it.