I've never done a track day that's not karting, but done a fair bit of sim stuff. I've written about my thoughts previously, starting
here.
TL;DR: There's starting to be a compelling amount of evidence that GT5/Forza/nkPro/LFS/rF/iRacing can, when used in a focused fashion, make you a better driver. Some titles can make you even better than others, for reasons including and beyond just the physics (incl. tyre) models.
And please stop making petty arguments over B. Heitkotter. He's proof positive that every racing tool has its value. He's auto-x'd, iRaced and GT5'd. Like anyone serious would do. Refer here.