Do you generally recommend that candidates go 'above and beyond' in preparing for interviews by, for example, putting together 30-60-90 day plans or a report on the company/product and strengths/weaknesses/opportunities to give the interviewer a glimpse into how they think? In which situations do you recommend this approach or not?

I don't have a recommendation for or against this type of detailed preparation, especially if it helps you structure verbal responses that also give a glimpse into how you think, problem solve and can be an asset to the company.

But I wouldn't focus on developing unrequested collateral at the expense of having solid verbal responses.

I would bring out supporting materials when they support your response to a particular question (ie if asked about what your 30-60-90 day plan would be in the role or what your organizational process is, show the prepared collateral as part of your response). Just be prepared for technical difficulties (internet bandwidth issues, screen sharing issues etc) that may impact how/if you can share these items in the interview itself.

And remember, if what you prepared highlights a particular strength that you bring to the role, then you could also include it in a "thank you" email as a follow-up to your conversation.