The fees are neglible either way. Their purpose is to prevent spam, so as long as we aren't getting spammed fees should be as low as possible. When BitShares has grown to the point where it has a huge userbase of people using the block chain primarily for practical reasons, rather than as investors, then it will make sense to increase fees also for the sake of earning revenue. At this moment fee revenue is nonexistent anyway and value is gained from getting new users to buy into bitassets.