Its a shame the cattery doesnt support a mini stay. I guess the benefit depends on your cats temperament, our younger cat is really timid around new people and I do think building her stay up helped her over the inital shock of the strange surroundings.
Even though its never nice leaving them (and our little one cries loudly all the way there in the car, just to pile on the guilt), as long as you are happy they are in good hands just keep reminding yourself they are at least safe and secure while you are away. Good luck!