I'm not keen on this one. It has a sensible reading as an injunction to keep the support of one's prior wide, and if that is what one is reminded of by the maxim, that is fine. But too often I see in everyday discourse people saying "you've made your mind up!" as a criticism. The argument becomes a bodyguard to support a belief that has no other support. Some Wikipedia scholarship indicates that the real situation behind the quote is unpromising for a clear moral about rationality. Cromwell made this appeal on the occasion of the Scots proclaiming Charles II their king instead of accepting Cromwell's rule. Being rebuffed, he conquered them, and it appears from this biography, p184ff that he would have had an easier job of it had he not taken the time to first invite their surrender. On the other hand, the Scots handcapped themselves by too strict an attention to the religious correctness of their generals and soldiers, at the expense of numbers in the field, and might even have benefitted from the lesser fervour that Cromwell suggested to them.

Currently, no. It seems worthwhile to keep old quotes visible, but I suspect that would be better accomplished by automatically generating a database of rationality quotes from these threads (like DanielVarga's best of collections), and then displaying a random one on each LW page with frequency related to the number of upvotes they received, say. I don't think that duplicating quotes in quote threads is a good idea, because this focuses effort on finding new quotes and material to incorporate into a growing body of knowledge rather than rehashing previously found knowledge.