Image stabilization is a great tool for handheld shooting (whether that's stills or video) as it provides extra support in steadying the frame and reducing blur caused by shaking.
In astrophotography however, it's perhaps not essential, as you'll always be shooting on a tripod which reduces the need for extra image stabilization. If that's the case, you can save yourself some money and opt for a less that doesn't have that (often costly) feature.
It's worth noting that while Canon uses the term Image Stabilization (IS), Nikon calls it Vibration Reducation (VR), Sony has an Optical Stabilizer (OS) and Optical SteadyShot (OSS).