Ok, let's analyze this a bit. You have a 2000 Box with 72K miles and a CEL showing a P0430 code. This code indicates a failed cat on the left side of the car. Checking the MAF, AOS and gas cap are always good maintenance checks but today they are probably unrelated. No mixture codes at all. You don't have a mixture/air leak problem you have a cat/sensor problem.
Three choices:
1. Add a bottle of Techron fuel additive and go for a spirited drive. You might get lucky and burn off whatever was causing cat inefficiency.
2. Replace the cat (rear-left side). Most likely fix.
3. Replace the aft sensor and cross your fingers that it was not reporting properly.
Here is a good description of how O2 sensors work:
http://sites.google.com/site/mikefocke2/oxygensensors
Good luck!