You don't really want to increase your waist size.
First off, you can have an extremely strong core, and still have it be 30inches. Do weighted ab exercises. Do oblique exercises. Do deadlifts for your lower back. I am pretty certain that doing all that, won't take you to a 31, 32, or even 33 inch waist unless you pack on some serious fat.
Advantages to having a smaller waist:
Easier to maintain that V taper
Girls aren't too fond of huge waists
Everything else looks bigger.
Easier to dodge projectiles...
Advantages of having a big waist:
You'll have a big waist?
Let's go with the negatives
DISadvantadges of having a small waist:
You may need to wear a belt.
DISadvantages of having a bigger waist:
You'll look thicker. In clothes, you'll appear to be 'fatter', even if you are muscular.
The bigger your waist, the harder it will be to find fitting pants.
Harder to acheive that V taper
Possibility of decrease core ROM
Bigger belts.
Everything looks smaller. (Chest, Head, Neck, Your D*ck.)
Which would you rather have?