My opinion doesn't really count because I do not own any of these two cameras and I have no hands-on experience in taking panorama / MF pictures. All I know I gathered from articles on the web and seeing the pictures posted.
I do not dislike the colour tones of either camera. In fact, in some of the sites I viewed, XPAN II's pictures are very sharp and colourful, though I have no idea whether they have been modified. Pictures taken by the M7 II are usually scenery and colours seem accurate and natural.
I have looked at and held both cameras. XPAN II is beyond criticism with its Ti body (TX2 is even cooler with the black colored). That said, Mamiya is also very solid, though it is indeed a plastic body.
I like the feel of M7II more because I have very big hands. It is not heavy with its size. XPAN appeals to me because it looks cool, girls will like it more.
I have a Phenix 50mm so the XPAN normal frame is useless to me. Like u said, 16K for a panorama camera seems too expensive. I will not buy the 30mm lens even though I have the money. It is just too expensive and I would be stupid not to use the money to buy, say a G2 set or a Hexar RF.
I wonder where they sell a hong goods in HK. M7II = great value for money !
http://www.uart.org.tw/pscl/kun/yushan/yushan.htm