I would agree that the larger you go the more stable and thus the "easier" it is to maintain a thriving system. However, it is much more expensive. Not only the up front costs of buying a big tank and big equipment but your evaporation will go way up, you will go through reactor media, co2, additives, food, and obviously you'll buy a lot more coral and fish.
It starts to add up rather quickly.
One suggestion I'd like to make, if you aren't already, is use LEDs to light it!