Nice photos. Lucky it wasn't raining this year
But nothing shot above ISO 1600? With the K-x you could have safely gone to ISO 3200 (or even higher, depending on your preferences), which might have helped score a few more keepers for you when using a slow lens.
Another tip with variable aperture slow zooms is to sometimes go a bit wider in order to let you open up the lens aperture a bit more, and then if necessary crop the resulting photo a tad.
Otherwise there's no substitute for fast primes like the FA 50 1.4 or even f2.8 zooms like the Tamron 28-72 for this kind of event.
A good flash can certainly be helpful but with the Mardi Gras parade there is a lot of ambient light around that you should be able to take advantage of with the right lens(es).