I've seen setups with and without starphire (or "low iron" since starphire is apparently a trademark of one company) glass that have been set up by the same people. I do notice a difference, but honestly, not a ton. Starphire glass seems to look the best in tanks that run halides and LEDs for some reason (again, just personal opinion).
I really wanted a starphire front on my new tank, but could not find one within a reasonable price.
Overall, is it noticeable, kind of. Is it worth the extra money? I'm not completely sure.