Parsley probably won't go to seed unless this is the second year you've had the same plant. Oregano doesn't readily go to seed for me, it's perennial. The basil will readily cross, and not all crosses are a happy thing. Genovese x thai queen is
. If you want to save seed from them I'd suggest only allowing one type to flower each year.
Otherwise I don't see any reason not to let the others go to seed. I use lost of dill and coriander (cilantro seed) in my cooking.