The only advantage to make a starter with two packs is if the packs are beyond their 'use by' date by quite a bit. Otherwise, a small starter (1 to 2 liters) will start with too many cells to promote healthy growth and it doesn't make sense to spend the extra DME, time, and energy to make way more new yeast cells with a larger starter unless you are going to split the starter for another batch.
Bob357 is correct that the added exposure for really no gain is just another vector for contamination.