However, since the question closed as duplicate can't be viewed by general public (they are redirected to the target question), is there any use in keeping these closed questions in the long run?
I'll admit that I was wrong about something when I proposed this. I had thought that the Roomba would delete these questions if they were downvoted and unanswered. However, it seems the Roomba does not delete questions marked as duplicates. So yes, if we follow this policy and don't put any effort into deleting the questions, we'll be left with a large number of posts which are duplicates of the tutorial.
Your question is "is there any use in keeping these?" and to that I think the answer is usually "not really". The questions don't contain any interesting new details. They might sometimes be useful for search engine optimization, and logged out users will immediately be redirected to the duplicate target. However, this is a rather rare case and hard to predict. They also might occasionally gain a bit of rep for the asker or an answerer, but that's not a big concern. There's also a rare case where the OP wants to find their question after leaving it for a while, which deleting would make harder, but that's quite uncommon if we wait for a few days before deleting.
On the other hand, we could also ask "is there any harm in keeping these?" and I think the answer again is usually "not really". If a user is insistently editing a question to get it bumped to the front page or flagging it to try to get it reopened, that might be a problem. But most of these are going to silently drop off the main page and then be basically invisible. It's unlikely they'll get a lot of activity, especially since logged out users will be silently redirected to the tutorial question. So long as the question isn't getting any views or activity, it's just sort of there, and doesn't really do much other than occasionally help with SEO for the tutorial.
So, in the end, I think there's little to gain or lose from deleting these questions. I don't think it's worth the effort to go through every time, but I also don't think it would hurt much if these questions do get deleted. I personally don't think it's worth putting in the extra effort to do this (it increases the number of required votes to deal with the question from 5 to 8 and only has a visible effect for logged in users who manage to find the question), so I wouldn't bother. But if other users perceive a real cost in keeping such questions around, I think there's little harm in deleting most of them.