There are no spot exercises that will help you reduce fat percentages in your body. The only way to lose fat (notice I did not say "lose weight") is through cardiovascular exercise and a diet low in calories. Basically, you should burn more calories than you consume. Cardiovascular exercise will first burn your immediate sugars and calories and then, after it has consumed the sugars, it will burn fat. However, you have to be careful because there comes a moment, if you do too much cardio, where you will stop burning fat and your body will start to target muscle mass for energy. This will severly deteriorate your muscles.
Now, regarding what I said above (losing fat and not weight), fat is much lighter in weight than muscle. So you might find that if you do cardio and muscle training, your weight might actually increase. This is ok because the ultimate goal is to reduce the fat to muscle ratio. You will be at less risk of heart disease and you will look better.
As for the larger muscle groups, yes. Larger muscles consume more energy and thus help to raise your metabolism (the amount of energy you burn under normal conditions) but this is truly a minimal amount compared to what you burn through cardio exercise. Personally, I do not do many crunches during my work out. At most I will do 3 sets of 20 crunches, twice a week. I make sure I use proper alignment during all other exercises and I notice that doing this engages my core sufficiently to have marked abs.