Well doing core work won't magically make your stomach fat go away, just as bicep curls won't magically make your arm fat go away, it's just tightening and expanding the growth of your muscles underneath the fat, sure you will see improvement because of the tightening, but the fat isn't just 'going away' because of that.
I think a routine is the hardest thing to do, or at least coming up with a routine. Because you don't want to overwork a certain muscle, or do too much work from one exercise, that can lead to all sort of problems like hemorrhoids(these suck, because they are so annoying), and strains. Both can derail you from exercising, and make you unmotivated.
Like you said it's just best to finally figure out what that routine is and stick with it, and once you master that routine throw in some new stuff to keep you on top of your game.
Plus I figure adding in new stuff down the road will keep you motivated, because it shows improvement.