I was wondering, sometimes the reason for the existence of a duplicate question might be, because the original was not very "findable." Or the duplicate might have better answers, or applicable to more circumstances. Are there any efforts to merge questions in those circumstances?
Less findable original
If the original wasn't very findable then thats exactly when a duplicate is a good thing to make it more findable. Which is the more findable is ultimately irrelevant as one will point to the other. The question is which has the best answers
Less clear original
Again as both questions point to the same answers it doesn't matter (much), the question again is which has better answers
Both have good answers
This is the case in which a merge is appropriate, flag for moderator attention to suggest this.
Don't take close as duplicate as a bad thing; take it as "hey! Good news! We've found all these ready made answers to your question! "
When we close a question as duplicate, we do because it is asking for the exact same thing and we judge that it won't get different answers.
Is there any effort in determining if a duplicate question is better than the original?
...If it is closed as duplicate, the effort has been made.
If it is clear that your question is not applicable to the same situations or might get different answers because there is a variant to it, it won't get closed.
I asked this one this morning about a question that was asked many times before but since it is different and there were no reputation tracker before, it is now a different question.
Merging questions certainly has happened in the past; that would happen only when you had two separate questions, both of which had very good answer(s) worth saving, which were determined to be sufficiently similar to not merit two separate questions. I'm fairly sure it's quite rare (in particular, a mod would have to do it; there's no 'merge' flag for a regular user, so it would have to come from an 'other' flag or a request from meta).
In general, the reason for the duplicate redirect (as opposed to deletion) is specifically because of what you say: perhaps the duplicate might be more findable, even if the original has answers (or better answers). Questions closed for Off Topic or other reasons are often deleted eventually; questions closed for Duplicate are not, so that Google/etc. index them and will bring them up in results if they are indeed well written questions.
The "is any effort used" of course varies by question... it takes 5 votes to close something of 3k+ rep users, so hopefully at least one of those users went to some effort. I would suggest that almost all of the time that is the case, but certainly occasional questions might get 4 robo-reviewers and one initial misguided soul.