I love Heritage. I am currently wearing the vintage Eau de Parfum today, a bit richer and luxurious than the EdT.
Yes, it's formal - but I am wearing it with khakis and a long sleeved shirt at my office, and I feel totally comfortable wearing it. Dated? I do not think of it in those terms, it doesn't smell like a '1992 fragrance'.
I do not like Bois de Portugal. But I love Heritage.
I do not think it is modern, but that's never been what I look for from Guerlain fragrances.
If you enjoy the way the juice smells, wear it!