I don't think that strict rules and close voting are a good way to enforce research effort. My big suggestions would be:
- Close conspiracy theory questions. Probably add a custom reason for this; it's common enough.
- Close general reference questions. Probably add a custom reason for this too.
- Close everything else that's known bad. "Too broad" and "unclear what you're asking" cover an awful lot of ground.
- Don't close otherwise good questions, regardless of research effort. Downvoting and asking for clarification and/or research is fine though!
I think the most important question to ask yourself when evaluating a question with respect to research effort is:
Would the OP still be asking the question if they'd done a little research?
If no, then it is indeed a bad question. I think the best thing to do in that case is downvote (after all, the site does explicitly provide this as a reason to downvote questions). If there are serious problems remaining (after dealing with conspiracy theory and general reference questions), that's where you can focus additional efforts.
If yes, then the question should be regarded as fine in terms of research effort, whether or not the OP actually has explicitly proved that they did the research. (Note that it could still be too broad, too unclear, and so on - all that is separate.) If the question can't easily be answered by non-expert research, then including a proof of that in the question doesn't actually make the question better.
The point here is to consider the merits of the actual question being asked, not just the degree to which the OP has attempted to answer it. If the question is "good", the site should be happy to have it, and if it's "bad", the site should be happy to get rid of it, all regardless of the amount of research demonstrated in the question.
I get the impression that you're trying to use research effort as a proxy for making those decisions about more specific bad categories, i.e. if the question goes away after asking for research, it must have been bad. But I think it's counterproductive to impose additional burden on good questions in order to weed out the bad ones.
To take a step back, I see that you're worried about attracting experts. That's a legitimate concern! And I agree, a good way to do that is to have really interesting questions!
However, I think there are a few disconnects between that and a "close without research effort" policy:
Lack of research effort isn't exactly the same as not interesting. Making strict rules here is a good way to throw away both bad and good questions, not just bad ones.
Making it take more work to ask questions, in general, discourages people from asking questions - the opposite of your goal.
Getting rid of bad questions increases the fraction of good questions, not the number of good questions. Even if you could come up with a rule that only got rid of bad questions, you still wouldn't really be making progress. (If you were taking an unmanageable 100 questions/day and pruning it to 50 good questions/day, sure. If the site gets there, revisit this! But right now the site has 7 questions/day.)