Great point On Arbitrage, never thought of that angle with the bet sizing. Getting a lot down though can be risky if you don't get approved on the second one or they change the odds before you can get them both in. Scalping on moves later in the day though are bad for your ROI.
There are a lot of ways to skin a cat. There are times when NFL odds comeout on Sunday night and a team is -2 and you feel pretty confident it is going to go to 3, this represents a lot more value than a regular move obviously. Regardless of your opinion about this game, it is best to hit the 2 right then and there. If it doesn't move then you could say it is a -EV bet, but that is just another element of risk/reward. A lot of value in just being able to predict market sentiment.
Also as far as hedging goes, when matchbook basically dealt like -102 it was a far better strategy. Matchbook was awesome for stuff like that. There is a lot of talk about legalization and if it did happen it wouldn't go to this extreme but I'd rather just see a giant exchange network with ample liquidity than anything else.
An exchange with liquidity would absolutely kick the books ass in a free market environment so therefore it is likely a no go.