I'm struggling to find a "rule" here, Paco! Cf. these common phrases:
1. That seems to be the case.
2. That seems to be true.
3. That seems likely.
4. That seems like a good idea.
5. That seems a good idea.
6. She seems a nice girl.
7. It seems quite easy.
8. It seems to be someone else's hat.
9. It seems the best thing to do.
All I can say is that "she seems (to be) perfection" would seem unusual in either form!
MrP