I think in the end his flaws as a candidate that we saw in 2004 still become a factor. His patrician manner, his inability to respond effectively to negative campaigning, and his lack of a set of strongly believed principles or priorities in domestic politics really don't augur well for him winning the White House.
These were not his decisive flaws. His decisive flaw, from the very beginning of his career, was that he was playing the veteran card, but an unusual version of it, the anti-war veteran card. It meant he would never in his career get majority support from mainstream veterans organizations, and there'd be tons of willing veterans, perceived as credible enough by part of the media, working to neutralize the strength he was trying to draw from him as a veteran.
Of the flaws listed in the above, I can accept his patrician manner had some significance, but that was baked into him from the very beginning of his political career.
I don't buy the principles/priorities argument. All winning candidates are at least as much chameleons as losing ones are. And I don't think tactics were Kerry's fundamental problem. Gore's defeat can be blamed much more on tactical causes then Kerry's.
Howard Dean would have seemed more principled, but would have lost by more. Jon Edwards could have been considered too lightweight. There were emotional forces in the US public beyond either campaigns control that better explain the outcome than campaign tactics.
