I guess it's kinda age dependent, besides that every parent-child relationship is different so as often as it's acceptable to all the parties concerned, I'd say.
No need to feel guilty for just being different and not exactly finding something to spend time with together. Visiting once a week is pretty often. As long as you're fine with that, it's okay.
In general, when you typically moved out as a late teen, or even in your twenties it's probably pretty normal to visit them once a week. Whereas I think if you're getting older and try to start your own family, or have one and are kinda busy anyway, then it may cut down to the typical birthdays, easter, xmas and so on. So several times a year, except some surprise visits.
If there is no problem that may keep you from seeing them, whether it's being terribly busy, living a big distance apart, or actually having a serious reason to avoid them.
As far as our typical western culture works.
In other cultures, such as Italian, it’s normal for extended families to live under one roof anyway. They’ve done it for centuries and they’ve kind of keep this tradition. Since it can work obviously.
As long as both sides feel fine, so not overrun and annoyed or ignored if it's the other way around or keeping someone away from their own family/friends it's pretty much okay.
I usually tend to visit my mother once a week. Otherwise I couldn't taste her wonderful cakes and pies... or I'd need to bake them by myself... Well no, then I rather visit her. The cake is worth it.