I apologize that this answer is so long.
I think we should add a new closing reason for question with insufficient research.
The main goal is to help users improve their questions.
There would be no real changes to our rules.
Requiring research is already a policy
We already require research effort for questions.
Some of it is based on our scope description, and some is built into the SE system.
Perhaps the question is to what extent we ought to enforce this policy.
Our help page on on-topic questions tells that you should not ask translation requests or etymological queries that show no serious research effort using readily available online sources.
(This help page is editable. There is a separate meta post about editing it.)
We already have a policy that research effort is required.
Our help page on reopening questions tells that if your question has been closed, you should be sure that you've read the close notice and any comments on the question so you can address any concerns raised there.
We cannot edit that help page, but we can make that bit of the page more helpful by making the close notice more helpful.
There is also a help page for quality standards errors, which tells that a question should include any background research you've tried but wasn't enough to solve your problem.
The how to ask help page also makes a clear point that research is needed.
Our tour also tells that you should not ask questions that show no research effort using readily available online sources.
The tour is editable.
(We might want to update the link in the tour if we have a better meta source for research requirements.)
Do we need to be more explicit about research?
I do not think so.
We can provide more help, but the current rules suffice.
I think it is already sufficiently clear that some research is required.
And if we add the new closing reason, we can communicate the requirement to those who missed that line in our tour.
I agree with Cerberus that we should have no unnecessary rules or bureaucracy on the site.
Requiring research is already a rule, and I would not make changes to the rule.
I have nothing against tweaking the rule a bit or discussing how it should be enforced, but I would not make major changes to the rule itself.
In my view the new closing reason would not add a rule, it would only add a means of communication.
What does sufficient research mean?
Sometimes it is hard to prove that you have tried to solve the problem yourself.
If you say "I googled for 30 minutes and found nothing", I am inclined to believe and consider the research sufficient, unless the question really is way too elementary.
If someone asks "what is a cat in Latin?" and claims that they found no translation at all, I would comment to give a link to some resources (maybe here) and close the question for insufficient research.
It can be reopened later if the user tells what they have found and indicates what more they want to know.
I prefer that we leave the guideline vague and judge case by case.
Like any guideline, requiring research is just a guideline.
I prefer to leave room for judgement.
There are great questions that utterly fail an on-topic criterion or two, and we should not close such things.
Telling users what to do
If someone asks a bad question, we should tell them how to improve it.
In addition, if the question is too bad to keep, we should close it.
If a question is bad enough to merit closure, we should make it clear what is needed to improve it.
The closing reasons "insufficient research" and "unclear" are close to each other, and low quality questions are likely to show symptoms of both.
However, if someone is asking a pure translation question with no indication of research effort, I would consider it very misleading to close the question as "unclear".
There have been questions that I would have liked to close for insufficient research although the objective was pretty clear.
Closure is always a result of overall judgement, not going through a list of a list of criteria.
If the overall judgement says "close!", then the closing reason should indicate what the key problem is.
Commenting is a good supplement, but the closure banner should be informative in itself.
One important thing to communicate with the closing banner is that the question can be reopened.
We can close more new users' questions than we do currently, provided that we make it abundantly clear that the questions can be brought back to life once they are improved.
That will also serve users: the answers will be more useful for them once they show their own thoughts.
This is related to the con point listed in the question.
What resources must users check?
As I said before, I prefer not to carve rules in stone, but we should tell users what kinds of resources they are expected to check.
I think the resources listed in the meta question about translation and homework questions are certainly enough.
With translation questions I would consider it sufficient to check any of the dictionaries mentioned in our dictionary list.
The relevant resources depend on the kind of question asked, and the expectation of research should (in my view) cover all question types.
Lack of research has been the biggest problem in translation questions, so we should focus there.
What to do?
As mentioned, I suggest creating a new closing reason for insufficient research.
If we decide to do that, the proper wording should be discussed in a separate meta question.
I hope that the requirement for research is enforced.
The suitable level of enforcement is left for everyone with sufficient reputation to decide — we, the users, enforce any policy we might have.