If you've been putting off going to a track but always wanted to, just go and do it. I put it off for way too long in my life and went for the first time last month. I had a blast! I have plans for a few friends and I to go again next month.
It's tiring, it's all day, but it'll put a smile on your face every time you remember it and drive your car. As far as compared to GT5, it's just not the same. Having the rear slide out from you, actually losing control and spinning, fear of said spin, and by your final run feeling like you're starting to get the hang of it...the real driving simulator just doesn't give that.