do I need IS?

...trying to figure out if I should be eyeing the E-410 or the E-510. : ) It seems that the three major differences of the 510 are: IS, extra size/weight, and costs $200 (25%!) more.

I take most of my photos outdoors, while hiking, cycling, and backpacking, although not necessarily in daylight. My current photography habits are governed by a tiny Canon S410 with 3x zoom that I rarely use fully extended. Sometimes I wish it had IS, but for everything other than actual night shots, I'm usually fine cranking up the ISO to 400 and holding carefully. Thus, I wonder if I can get by without IS on the E-410, which according to Phil's review has pretty good high ISO, and every gram counts when you're backpacking. On the other hand, (1) the kit lens is slower than the f/2.8 of the digicam, (2) I might get to like using high zoom, (3) everyone seems to think getting body IS for $100-$200 is a bargain.

How much use is IS in my situation?

thanks for any advice.