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It is very plausible that the upstream o2 sensor was causing the car to run rich, which is where the un burnt fuel comes from. Replacing the o2 sensor is part of that equation but your timing is another. If both are good then you don't have anything to worry about.
I have never heard of cleaning a CAT. Once clogged up and unable to filter the air you should scrap them. They bring tons of money. Anywhere from $50-$150 depending on size and weight. However, since your states emissions standards are more strict I'm not sure how you go about replacing a CAT. If you can do it legally then a direct replacement would be the way to go to avoid modifying the exhaust system. I doubt the CARB guys would want you switching your manifold and CAT placement, as you said. But, sounds like it passed last time so there is no reason to replace it until it fails.
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