Here's the thing- lets say you want a competitive deck that has black in it. That means you are going to need 4 Thoughtsiezes. Thoughtsieze is a 15 dollar card. If you wanted to buy 4 copies, its going to cost you 60 dollars. For that same price, you could enter 4 FNM drafts. You are going to get a chance to crack 12 boosters across those events, plus any that you win. There are 53 rare cards in Theros.
Yes, by drafting, you will get more cards, but it isn't likely you will get ones you actually want for your deck. If you enjoy limited, I would play limited. If your goal is to take 500 and make a competitive deck, then you are going to be buying singles to achieve that goal.
I am thinking I'll do some limited just to get back in the "swing" of things unless the meta game for limited is very different than standard.
Do most compettive players even crack boxes anymore? I guess they just look at the spoilers for the sets and build out that way.