Regarding #1, for some people, the opposite happens: because the idea is out there, executing becomes less important. So YMMV. I personally feel that one part of executing is indeed to get validation on the idea itself. By discussing it, one might get early validation from friends ("oh yeah, that's a good idea!"), which can seem good enough because it validates that you can have good ideas, that you're not crazy for finding a problem here and that you're smart for finding a solution.

As for the idea journal, worst case, in a few years you can look back at all these ideas that you had, did not execute on and that somebody did with (some) success. Happened to me just today :)