I would consider the Audya 4, but the Plus is such a convenient size and weight that I hesitate making a change to a unit that is double the size, weight and price without offering double the benefits and features.
Jerry,
I agree on the size and the weight, but with the Midjay Pro out here in Italy there are used Audya 4 on sale for 1600-1800 euros and I bet that the same will happen as soon as the Midjay arrives to USA. Besides, the Audya has five times more audio styles with much longer loops, audio guitars, etc.
All in all to me a second hand Audya 4 seems a better investment.