I'm cautiouslt optimistic. You get XP by levelling them AND by collecting decor AND by releasing them. I already release a significant amount of restaurant and salon pikmin, it's nice that now I'll get something for it.
What's not clear to me is whether or not this allows us to upgrade pimkmin from regular decor to rare, or whether (like the former restaurant system, clover pikmin, train pikmin) it's only new decor gifts that might be rare.