Sometimes when there are duplicates, the newer question gets answers that are relevant and weren't mentioned in the first question.
If merging is not suitable (for instance, a relevant answer would get hidden in a ton of other answers), I think that adding a link on the old question to the new question might be helpful for people looking for answers.
Especially if the question is asked on a different time (meaning a different crowd answering) or asked a big while after the first question (new developments might have occurred.)
Something like this might serve this purpose better, but looks a lot more complex to implement correctly. What I propose should be easy to implement as a temporary measure at least.