1. Regarding Rasmussen's indication that Condi has high approval ratings: many potential candidates have high approval ratings before entering a race. Rick Perry, Sarah Palin, and a variety of others had much higher approval ratings while waiting in the wings than when they actually campaigned. After a candidate enters the arena and people get to know them better (and their opponents' ads begin having an effect), they naturally become less popular. In Condi's case the deterioration in popularity will be due to reminders about her time in the Bush Administration.
2. Further, the Rasmussen numbers are almost certainly not representative of the general population, given that Rasmussen consistently over polls Republicans. This isn't a bald assertion: in the 2010 elections Rasmussen consistently overestimated the standing of Republican candidates and produced the least accurate set of polling results ever, including (most famously) a 40 point error in the Hawaiian Senate race.
3. Once Condi gets into the race, the Obama team will easily paint a Romney presidency as a return to neo-conservative principles, especially given that his foreign policy advisory team already comprises a variety of neo-conservatives from the Bush Administration. I'm confident that, given it is largely because of these principles in action that Bush is literally the least popular president since Nixon, and given that Condi's input was integral to most of the foreign policy decisions Bush made, her addition to an already neo-conservative laced team will be a net liability.
4. Finally, if I were a Chicago politician that was willing to do anything to win, I'd use Condi's closeted homosexuality as a wedge issue to cleave more conservative Republicans from the Romney campaign, especially given that they are suspicious of his conservative credentials as is. Obviously, this wouldn't be pointed out in any ads at all associated with the Democratic party or the Obama campaign, including pro-Obama Super PAC ads. Instead, the intel on Condi's relationship with the woman she owns that home with and the credit line they share would conveniently start making the rounds among conservatives at some crucial juncture or other.
This could be enough to freak out a fair-sized contingent of the more conservative wing of the party and thus cost Romney a decent chunk of vote share. In an election that is largely going to be about maximizing one's partisan support rather than attempting to be overly centrist (ala the 2004 campaign), this could be important and ads to Condi's net liability status.
Jindal seems more likely because he is still a minority and the son of immigrants and yet has a bunch of legitimate experience (more than Rubio) and conservative credentials, without any obvious liabilities.
