Yes - my kids got good insights at off time visits.
But I think what you’re getting at is - we can’t get there in busy times so is it ok to go when it’s not as busy/robust.
We did - and if the alternative is not going, then yes - you will get a lot out of it.
I don’t think my student would have had a different take on a school and the surrounding area based on the date/timing visited.
You still see the campus, buildings, surrounds. You can still make appointments to see folks and you can still stop folks on campus to ask questions, etc.
That said, there’s only so much time on the calendar and if you truly want to get out and see many - your choice is to see them whenever you can or not at all.
And in that regard, yes it is helpful - even in summer.