My Opinions and Recommendations
I loved En Vogue before they were three. I still think that Funky Divas is one of the best albums ever made. The four had so much soul and they practically defined the later developed girl power movement. I love Free Your Mind and My Lovin' (You're Never Gonna Get It), the two singles off the CD. These girls carried the girl bands of the 80s power into the 90s.
Destiny's Child certainly gets a lot of its moves, looks and content from earlier bands like En Vogue, so you should definitely check them out, especially their Writings on the Wall CD, which carries a speak over in between songs, similar to that in Funky Divas. Also take a look at Tatyana Ali's album which shares the same pop content and sound as En Vogue. Finally, look at the queen of soul, Aretha Franklin, who I am sure provided much inspiration to En Vogue.