As my smallest PA solution for small churches or background piano music in smaller rooms, I have replaced the Bose Soundlink Air (virtually identical to Sounddock portable) with the even better sounding Klipsch KMC-3.
http://www.klipsch.com/kmc-3-wireless-music-systemIt weighs 3.6 kg (about 8 pounds) and is small enough for a large backpack. It gets as loud as the Sounddock portable, but has a more open mid-range sound and better, deeper, cleaner bass. Astounding big sound! Klipsch states a total of 65 Watts RMS, and that's certainly at least what it sounds like.
BTW, this is a great website for comparing various small consumer speakers like the Klipsch, the speakers were recorded with a high-quality recorder, and you can switch between the speakers:
http://switcher.oluvsgadgets.net/