As far as I understand (and I'm always open to correction from people who are polite and civil
), the 1Ds would not have significantly less noise that the 10D on balance so this would not be a good reason to upgrade from a 10D to a 1Ds.
In fact Michael's review of the 10D makes mention of the exceptional lack of noise at and above ISO 400, implying that it's superior to the 1Ds in that regard.
The graphs at dpreview also show the noise levels of the 10D are significantly less than those of the 1Ds above ISO 400, although there is no direct comparison. One has to go through the circuitous route of comparing the 1Ds with the D60 and then the 10D with the D60. In fact, surprisingly, up to ISO 800, noise levels of the D60 are as good as or slightly better than those of the 1Ds.
However, there is a complicating factor. These dpreview noise tests are based on a pixel for pixel comparison. In practice, the real world comparison would be between 11MP and 6MP. This would have the effect of tipping the balance in favour of the 1Ds at ISO's below 400 and at least partially negating the noise advantage of the 10D above ISO 400.
If you are happy with the 10D noise levels below ISO 400 I'd see no reason to upgrade on this basis. The sorts of factors that would attract me to the 1Ds (I own a D60 and 20D) would be better focussing, ability to focus at f8 and of course higher resolution. The extra weight I could handle
.