Tactically I wouldn't really call it a blunder. If successful it would bring Kentucky into the Confederacy at most, and at least draw Buell out of Tennessee and give relief to the State from war right at harvest time, a big consideration.
Politically it was a sensible maneuver. It was right at the same time as Lee's offensive into Maryland, and though delayed a bit, the same time as Hindman's offensive into Missouri, (which got stopped at Prairie Grove in Arkansas and stayed behind schedule not happening till late Nov. early Dec.), and all that on paper would make the CSA look to be in the ascendant, and almost unstoppable in the press, thus potentially gaining politically in Europe. The Confederacy on the offensive everywhere at once, in theory winning, and thus looking to win the war at best, giving a temporary respite from Yankees to farms and other producers right when food and material is needed at most at the worst.
I'd say it was a sound gamble, that really could've gone either way in Kentucky till Perryville. Vicksburg still looked impregnable at this stage of 1862, I think it would've been felt it could even help the situation in Mississippi and probably did.
I think the bad part of the equation was Bragg, who given a choice between winning and losing, was gonna chose losing.