Windmill isn't particularly valuable for the attack ability for elves. However, the stats are irreplaceable. And, most of the stats come from the upper ranks of the skill. Going from rF-r9 WM will only net you 9 strength and 21 will, but going all the way to r1 will get you 30 strength and 50 will. The thing most elf players fail to grasp is that everyone has to melee sometime. So why would you want to go about it with little to no capability? Without putting in a whole lot of effort (elves have the AP charts easier, but the skill training reqs tend to be a bit harder) you can cap the vast majority of strength-adding skills.
That being said, do I think you should take the route of a melee elf? Hell no. It's not worth the trouble. However, like with all other races, windmill should be a priority skill. With the release of the destiny system, it's not even particularly hard to rank at any rank anymore. Beyond that, prioritize other irritating/difficult to rank skills such as refine, animal taming, mirage missile, etc., and have fun with it lol.