You say "if" you were "way serious", well if your training schedule and goals is NOT serious, I just don't know what serious would be, some obsessive non working person who didn't have to shop, cook, pay bills, etc who could do triathlon full time...and I mean FULL TIME
I like the idea of not building in a day and then doing whatever your body tells you to... I think that is what I do. For example, this week, I had an olympic last sunday, traveled monday, trained without stop from Tuesday, and thought of taking the day off today (Monday), but didn't, didn't feel like it (felt extra motivated), so my body is telling me "we are ok", and if I take every other day off this week, no problem. Then when I am not motivated, some extra days off won't matter. Of course this is untested un empirical training philosophy, but works for me.
ps, your swim time kicks butt, I hope I can do my HIM in that swim time.