The statement "When you don’t have much to go on, and limited resources, it’s better to aim at problems that you know are out there. Those things will lead you to new discoveries." which you say doesn't make sense to you, is exactly meant to promote "serendipitous" discoveries while looking for something else.
A bigger collider does not, in fact, have anything to look for, and so the only possible benefit it could yield is such "serendipitous" discoveries. But how many of those could there really be when you're essentially doing only one thing?
The point of the article is that the ridiculous amount of money, which a bigger collider would cost, is much better spent on a large amount of much more varied research activities, which do have concrete things to look for, but also have the potential for serendipitous discoveries. And since those activities are much more varied, the total potential for such discoveries would much larger as well.
A bigger collider does not, in fact, have anything to look for, and so the only possible benefit it could yield is such "serendipitous" discoveries. But how many of those could there really be when you're essentially doing only one thing?
The point of the article is that the ridiculous amount of money, which a bigger collider would cost, is much better spent on a large amount of much more varied research activities, which do have concrete things to look for, but also have the potential for serendipitous discoveries. And since those activities are much more varied, the total potential for such discoveries would much larger as well.