I loved Katee Sackhoff as Starbuck - the character and gender swap sure worked well for Battlestar Galactica.
Story, character, acting and making sure all of those work together is imperative and should be the driving force.
A female Starbuck worked because it was a reimagining of the series - the basics of Starbuck from the original series were "...Viper starfighter pilot, gambler, womanizer and smoker of "fumerellos," or cigars." While there was more to him than that, those were basics - take out womanizer and it applies to Kara Thrace. It had also been 30 years or so since the original Battlestar Galactica aired when the reboot happened.
Dr. Smith was pretty much genderless in Lost in Space. His traits weren't specific to a sex, race or anything, really. Add the fact that the series hasn't aired first run in almost 50 years... well, there's not a whole lot of folks out there who see it as little more than a quaint, family friendly series with not a lot of substance.
Fantastic Four I find a little different - while they attempted to explain the Johnny/Sue relationship, it fell flat. FF has been running in comics for years and years - and then there's the **** poor film they made around the Jordan and the rest of the cast.
I'm ticked about what they did to Superman in Man of Steel and BvS and they didn't bother to change his sex, ethnicity or much else.
Posey is solid actress. I just hope they give her solid material and make a good series around her.
Your mileage may vary.