I recently did a small white wool rug i have at home with powerburst simply because its what i had in the prespray bottle i was not impressed with the results at all, wondered if its because it is not designed for wool, but you say you got a good result and rinsed it well did you vacuum thoroughly, i always thought that quick resoiling was due to leaving residue in the carpet.
I did a friends house and his carpet was white i went back to return some rugs i had taken away to clean and the carpet from the kitchen to the hall was soiled again and he mentioned resoiling etc i just said that he is walking the dirt back onto the clean carpet and it will be more noticeable than when it was filthy.