Smart Keyboard reply:
I have the 10.5 iPad coupled with Apple's Smart Keyboard. If this keyboard didn't exist I would get along just fine without it. However now that I have it I wouldn't want to give it up so (for me) it is worth it.
With a quick unfold, it is always there when I need it. I can produce text much faster with the Smart Keyboard then I can typing on the virtual keyboard (dig the up, down, left, right arrows too). Having the virtual keyboard appear when the Smart Keyboard is folded up or disappear when the iPad is placed on the magnetic cradle is intuitive. I have no qualm with the viewing angle in typing mode. A second media viewing angle can be achieved with the keys folded back facing away from the back of the iPad. This is a more perpendicular angle, which I don't use as the typing angle is versatile (for me) and the whole platform is more stable with the keyboard in play.
The Smart Keyboard isn't as easy to peel away from the iPad as a Smart Cover due to the lack of that second bendable joint, but not difficult. As far a weight goes the Smart Keyboard for the 10.5 is just over 8 1/2 ounces, compaired to the 9.7 version Smart Cover weighing in at just under 3 ounces (don't know the 10.5 Smart Cover weight off hand). An additional 5 1/5 or so ounces is not a biggie to me.
Virtual keyboard reply:
Yes, IMO it is worth it.