Closing questions of the same pattern... (wiki)
If we only ever closed exact duplicates, there would be very few of them.
Closing instances of the same pattern against the canonical Q & A is beneficial; we should continue to do that. The question author gets pointed to a great resource that should solve their problem, and our ability to answer search engine queries is enhanced by having a different phrasing of the question. Closure as duplicate without answers results in an immediate redirect for anonymous users.
...or answering them for the use case (forum)
We already have a system for this.
The first vote to close as a duplicate will alert the question author to the existence of the potential existing answer. The author has a binding vote to close as a duplicate if it solves their problem:
If the question is different, it is up to the question author to make it clear in the question why that is.
Meanwhile, other users can vote to close (via the review queue as well as directly) or answer the specific question as they see fit. Either or both of these actions is acceptable, in my view.
Where the question is immediately marked as a duplicate by a gold tag badge holder...
...the message shown to the question author is different, but the process is much the same:
The first question edit after closure will trigger an automatic reopen review, so we can assess whether the closure as a duplicate was correct or not. Again, the onus is on the asker to make the case.
If all else fails, the question author can always ask a new question, noting the existence of the related Q & A, but making it clear which specific aspect they still need help with.
Often, there is no way to know (from the question alone) whether the asker is simply unaware of the pattern and general solution, or has tried it and failed to apply it in a particular instance.
We are not psychic, so there has to be some indication in the question that a specific solution is required. We're reasonable people here. I'm sure we would co-operate to reopen the question briefly to allow such an answer to be posted in edge case scenarios.
This is all easier now that gold badge holders can dupe close and reopen with a single action.
There is always a certain tension between the forum and wiki aspects of the SE model. All possible outcomes noted above seem OK to me, so I don't think there's a need for a rigid policy here, beyond current practice.
Related FAQ: How should duplicate questions be handled?