I like Candy Givens' voice, though I couldn't listen to her all day. The similarities with Janis are obvious, but Candy also has a certain innocence still in her voice - Janis sang like she had experienced a lot of things, I actually find listening to her less demanding than listening to Candy. And I hear more archaic (or 'real') country in Janis' voice. But to the casual listener, yeah, they do sound very similar.
But Candy could do more than just turbo voice Janis impersonations, she also had a distinct Carol King influence:
Mark Stein's connections to Deep Purple weren't just via Tommy Bolin: Vanilla Fudge were early DP Mk I's musical role model, as Ian Paice once said "we wanted to outfudge the Fudge, I don't hink we ever did". Like the Fudge, fledgling Purple attempted these grand rearrangements, this one even found grace with John Lennon who liked the version:
And in 1975, Mark Stein was one of the many keyboarders that auditioned with Blackmore's fledgling Rainbow.
I think history has been unkind to Vanilla Fudge and they have very much been forgotten which is unfair - their band sound was as influential as, say, Cream's, at least for keyboard-oriented bands. Without them, I doubt there would have been an Iron Butterfly, a Bloodrock, a Deep Purple, a Kansas, a Warhorse or an Uriah Heep. My pet theory why they were forgotten is that they mostly didn't write their own material - the same fate as The Hollies, Three Dog Night, Rare Earth, early Doctor Hook & the Medicine Show or Manfred Mann's Earth Band, who all excelled in doing "better-than-the-orginal"-covers, but dried up when it came to writing own songs. Having your own canon of songs written by yourself provides longevity for a band. Weirdly, the same doesn't apply for solo artists or no one would still be talking about Elvis or Frank Sinatra today.
Still, their iconic slo-mo arrangement of You Keep Me Hanging On was regularly carbon-copied by other bands: