I think playing with dolls is a good use of the child's imagination. My daughter would concoct all sorts of imaginative play with her Barbies, Polly Pockets, Bratz etc. but I was beyond bored within a few minutes of playing. Since she was an only child I was also her primary "playmate" so I felt bad about not liking to play dolls. I think its easy for kids to enter their imagination, I did alot of that as a kid, but as adults its not so easy to "transcend reality" like that. Its too bad, I could use that skill today ;)
As long as she's ok playing on her own, I wouldn't feel like you always had to play with her in these sorts of activities. I started encouraging more play dates with other kids my daughter's age. That way, they can play dolls and I didn't have to feel bad for "not getting into it."