+ 1 to Heretic's post above!
1. Anybody have any experience with the Kawasaki Accessory handlebar bag?
Yes; have 'em on '07 KLR650 (fits, although cataloged for Generation 2 KLR650's) and on '03 KLR250; two years or so of service.
2. I have been looking for the dimensions of this OEM accessory.
I don't know, man; maybe you can get an idea from images on the Kawasaki website; but . . . it holds more than you might imagine.
2. Does it block the view to the gauges?
No, not in my experience.
3. Does it impair access to the ignition key?
No, not in my experience . . . hey, it's a BAG! Like, made of flexible FABRIC! Since it's flexible . . . you can nudge the bag away from the fuel tank cap when opening and closing the cap.
4. What is the volume of this bag?
Will hold Multi-tool, Nebo tool, tire patches, digital camera, tire gauge, flashlight, etc., etc. Dont' think the cubic centimeters or cubic inches would be particularly meaningful, given the SHAPE of the bag . . . holds Granola bars . . . zip-ties . . . 'most anything than might come in handy.
5. How does it attach to the handlebar cross bar?
This is the most important and meaningful question you've asked!!!!!!!!!
The velcro straps MUST embrace BOTH the handlebar AND the reinforcing bar simultaneously, for the bag to assume its designed (and effective) shape!
Kinda hard to put into words, but . . . DO NOT fasten the velcro ever around JUST ONE BAR; instead . . . loop them around the parallel reinforcing bar (top) and handlebar (bottom), FASTENING the velcro only at the bottom, below the handlebar . . .
Seems kinda pricey, but the bag's a classy accessory; most useful, in my experience. As mentioned, works on Generation 1 (although desgined for Generation 2); might get a little more wind buffeting on the older bikes, because of the absence of fairing area, but . . . it works.
The velcro mounting seems rather robust, but . . . some zip-ties might add redundancy, in the event of a high-G spill.
Kawasaki got this one right, IMHO; YMMV!