Imeo
The way I see it you already do the best of both worlds. The last 2 preorders I took place in you also sent extras to your sellers for people that didn't get to preorder. Personally I like your preorder system I feel it is a lot less stressful than sitting by the computer waiting for the sale to start, hoping you get an order in before the site crashes etc. If you check the forum often you know when a preorder is going to happen (same thing you would have to do with no preorder system) to know when a sale will take place. This is just my opinion but I do like your system as it stands.
P.S.
During your last preorder for the stealth I decided not to order one during the preorder and then changed my mind when they were released, I was able to pickup one of the extras you sent to COV, so as I said the best of both worlds.