I don't know if Benoit and Guerrero would have made an impact in TNA. But in Benoit's case especially, going to TNA would have been best for him and WWE.
I read somewhere that Benoit was very close to signing with WWE in 2006. His contract had run out, he was needed at home to help care for Nancy and his son (since their son, Daniel, needed full-time care) and the temptation of a better schedule, which would allow him to be home more often and have extended his career, was very tempting. Also, Jeff Jarrett wanted to sign Benoit, and re-ignite their Ladder match series from WCW.
But Vince McMahon offered a better contract. Apparently, Vince offered Benoit the world, but only after Benoit signed, Vince reneged on a lot of his promises. Vince had no intention of pushing Benoit, but just re-signed him, so he wouldn't lose him to TNA. Remember that Chris Jericho was on his hiatus at the time too, and Jarrett planned to sign both Benoit and Jericho to TNA.
I am not saying that, if Benoit was in TNA, he, Nancy and Daniel would be alive today. I think that, with years of steriod abuse and head knocks, he was too far gone for the incident to be prevented. But if Benoit had gone to TNA, WWE wouldn't have got as much press over the murders, as it would be TNA who would be copping it instead.