[Monkey Wrench]

I'd use leather, get it wet, stretch it oer to get the shape, dont start gluing until it fits. then maybe start in the middle outward. if you need to you can do some sewing. i was surprised when I did it that the leather would conform quite well when wet and retained the shape as it dried. You might try covering a football or something as a test of your technique. the leather doesn't have to be thick but I'd use top leather not split leather that has a finish put on to look like it is top leather. I don't think using a few neat stitches is necessarily very visually detracting, but it is straying a bit from original.

leather only comes so big , you may be able to do it in one piece , with mine I made a sewn joint down the middle because, being on a budget I just used a ladies long coat from a thrift store for the leather.
the coat was tan color but I used black leather dye and that was dead easy. I followed it with a (Tandy) leather product that gave luster, which I washed a bit and encouraged it to dull down a bit after.. I'd also say if it is too shiny you can get reflections on the windshield and that can affect visibility.

If the car is being shown and judged for originality, then I'd try to repair the vinyl with a cover or patch as it may loose brownie points, but for an every day driver that is not a show car I think using real leather is a practical and reasonable alternative.

I'd fill any cracks or they will telegraph through , but leave the existing. vinyl in place.