Forget about aperture. A better way to think about image stabilization is that it gives you something like the equivalent of bumping the ISO up without incurring any noise penalty (for static subjects).

If you need, say, f/8 to make the picture you want to make (in order to get the right depth of field), then you need f/8. It doesn't matter what the maximum aperture of the lens is if it has to be set to f/8 to get the shot. In order to get the correct exposure, your remaining two variables are the sensitivity of the recording medium (the ISO) and the shutter speed.

As you increase the sensitivity (ISO), you will, of necessity, be reducing the dynamic range of the sensor and increasing the noise. Current-generation digital cameras are bloody amazing in terms of what they can do at high ISOs, but they will create better images at lower ISOs (provided, of course, that the image has been properly exposed). So cranking the ISO up is not always an option.

No matter how steadily you can hold a camera, you aren't perfect. You're not even as good as a tripod. In the 35mm film days, we used 1/(focal length in mm) as a rule of thumb for the slowest shutter speed you could use hand-held with ordinary films. (With high-acutance films like Kodachrome 25, Ektar 25 and Kodak Technical Pan, that would often be too slow.) That assumes full-frame 35mm film images and image enlargements that rarely went beyond 11 by 14 inches. These days, you're as likely to use a crop-sensor camera as full-frame, your sensor can record as much detail as the sharpest films, and if you print, your prints are likely to be larger. So the rule of thumb goes up to 1/(some multiple of the focal length in mm). If your lens is set to a 50mm focal length, then the slowest shutter speed you'd want to use hand-held would probably be in the neighbourhood of 1/125s (unless you are very practiced and steady). Any longer than that and the angular displacement of the image on the film/sensor caused by camera motion would be visible in the image.

Image stabilization means that as long as you are not trying to freeze subject motion, you can use a slower shutter speed at a given focal length. The IS/VR will compensate for camera movement. Somewhat. That means that you can use smaller apertures and/or lower ISOs than you would be able to use if you had nothing but the shutter speed to restrict the effects of camera movement.

If, on the other hand, narrowing the depth of field or freezing action with a high shutter speed is your aim, IS/VR won't help at all. You need a wider maximum aperture, either to reduce the DoF or to let enough light into the camera that you can use a higher shutter speed.