I have to admit, I love your posts. Keep 'em coming.
With the new G10:
Look at the EXIF info from your G9 shots. What focal length were the majority of your shots taken? If you see many at the widest angle, maybe the G10 will help you get the wide angle shot that the G9 couldn't. If, on the other hand, most of your shots are beyond 160 mm, consider the purchase of a G10 might be money better saved, in this time of the stock market affecting our buying.
For me, a wider angle is valuable. What I like about the G10 range is that it covers:
28 mm which really is only a moderately wide angle - I love landscapes!
35-50 mm which are normal focal lengths — some of the best, historically, are here!
85-135 which are portrait focal lengths — the art of capturing, expressions, moods, and juxtapositions of the face, hopefully with great background their.
(Admittedly the G7/G9 should be better with bokeh due to their longer focal lengths)
The G10 seems to have changed many things, save a more telephoto lens:
a new, wider/shorter lens (not reviewed)
a better grip
an improved viewfinder (guessing smaller coverage, but no lens interference)
a much higher resolution LCD (better than the XSi/40D, but not 50D or 5d Mark II)
a better control set (especially the new exposure comp. dial/repositioning of ISO)
a new chip, Digic IV, (which hasn't been professionally reviewed)
an improved battery
an improved auto focus
faster maximum shutter
longer flash reach
Other things to consider:
According to a test done by Don Ellis:
http://forums.dpreview.com/forums/read.asp?forum=1010&message=25698205
The G7/G9 lens is f 4.0 at 140 mm, whereas the new G10 is slower at f 4.5 at 140.
The G9 is proven. It has been demonstrated many times on this forum, in positive reviews, and in the media; it has been the choice of the majority of professional photographers as a portable digicam.
It has less pixel density.
On the other hand:
As with most higher end digital cameras, there have been some with problems... reported dust, pixels, etc.
The G10 is not proven.
What to tell the wife, if you decide to get the G10; the G10 is about the price of a lower end consumer lens, for the SLR system you used to own.
Don't tell her the lens would make substantially better photos or would retain its value better, all because you don't want to carry less than a pound more (the weight of an XSi with a kit lens, which I think you should consider)
Dave