Singular vs Plural – Should Prices Be Used in the Following Sentence?

This is one of those strange exceptions to the rule in English - it's not correct, but it's well understood by native speakers.

Normally, you would expect the plural to be used - multiple weddings for multiple couples - but it doesn't scan as well when read/spoken. This occasionally results in conflicting plural/singular for a handful of phrases where it 'feels' nicer to say it in a particular way.

However, in the example, while it refers to multiple brides and grooms, it refers to their singular wedding day. Readers would interpret this sentence to understand multiple couples and their respective single day.

Strictly, the singular day could be shared by all the people or could be a different day for each person. However in this sentence one considers each person as an individual because it's very unusual to have a shared group wedding ceremony.

It may also be inferring some brides and some grooms, in various combinations. The unfortunate thing about this particular example is that it requires some awareness of recent history in context of marriage practice.

In a pure grammatical sense, the start of the sentence is wrong. For clarity, I would write,

In the seventies, the bride and groom often stayed apart on their wedding day before the ceremony.

The use of "brides and grooms" in the example implies that most/all unmarried couples behaved in this manner, and readers would understand this given context. While it's not grammatically correct, it's one of those evolving aspects of language we can't really stop people from using!

There is a subtle difference in your two examples and I don't think they mean quite the same thing. Street can be used literally to refer to a paved road. Street can also be used to refer to particular things that that are outdoors or occur outdoors. Here in the U.S. homeless people live on/in the street or streets. You may say either. They both mean out of doors or unsheltered.

If I say He puts on his leather jacket and ventures into the street(s), I would generally be saying ...and ventures outdoors. This is different than saying He went into the street and starting clearing downed trees from last night's storm, which is a literal reference to a paved road.

When referring to literal, paved roads you will want to pay attention to the plural form. The street is covered in oil is different from The streets are covered in oil. When referring to outdoors you can use either street or streets. In that instance they mean the same.