I'm not sure I've noticed the price of Canon's going up unduly when they introduced IS, rather it seems all this is cheap technology nowadays.
And how much bigger have cameras got when IS was introduced, in fact is there any camera that has been noticably bigger than its non-IS cousin? I'd say that generally speaking when a manufacturer has introduced an IS camera its always been smaller than its predecessor.
As for being worried about battery life, well, it may be a consideration if you thought Leica may just bolt IS on to an M9 without thinking about it. Is it really likely that Leica wouldn't consider that?
Steve