The best advice I have been given is to be sure you love the dolls you pursue, or enjoy the process, or both.
Doll lovers all have particular reasons why they gather these little (and not so little) replicas of humans and creatures.
For some collectors the value is important. For some it is "vintage", or "modern" that is important. For some it is the dolls by particular doll designers they pursue. For some it is the motivation to express a skill-such as sewing, knitting, repainting, or photography.
Doll collecting can be the way to a career, a method of supporting a family, a legacy for your children, a reason for social interaction, or a simple hobby.
Whatever is the reason we do it, doll collecting offers a promise of some kind of satisfaction.
And if we are good at it or enjoy it, the promise is fulfilled...