A badly scratched windshield is not only annoying but a potential hazard. Sunlight, or even other lighting sources at night, give excessive glare impairing your overall visibility. Depending on how deep the scratches are many products on the market will give mediocre results at best. As long as the scratches are not deep enough to catch on your fingernail, you should be able to improve them. But hand buffing them out will be difficult. You can get it to be much better with a machine buffer and multiple passes, as needed. Products that provide nano compounds will work best to fill in the scratches.
Glass polishing is still not a mastered science, even by automotive detailers. But I suspect in the next ten years or so that will change. To date, only products with cerium oxide seem to be effective. I would look for something in that area. Give it a shot. Good luck and if you are able to try it, post back with results.