I think I let myself fall into the "grass is greener" mentality too much. I had the 18-55, sold it, and have thought about getting another. I've also thought about renting a 16-55 for a test drive. Just out of curiosity, I ran some simulations on camerasize.com. The 16-55 is 106mm x 83mm, and it weighs 655g (about 23 oz). If one carried all of the current f2 primes (18mm, 23mm, 35mm, and 50mm) in one's bag, the total lens weight would be 666g, with the heaviest lens, the 50, at 200g. I'm sure that makes a huge difference in camera handling, as opposed to the massive 16-55, which has very nice IQ.
So it comes down to size and convenience vs. compact handling. All of the primes I have or had displayed excellent IQ. The 18-55 was very good, too. It would be great to have excellent IQ, weather resistance, and never have to swap lenses, but the size and weight might be too high of a price to pay.
If only we could talk Fuji into a 16-55 f4 WR.