Any gas burning appliance (water heater in your case) needs to get fresh air from somewhere, and vent the exhaust somewhere outside (venting into the house is deadly).
Since it is in a utility room with a door that is closed most of the time, you need some kind of vent to get fresh air. You can pull that fresh air from either the (1) insulated living areas of the house, (2) uninsulated/unoccupied areas of the house (attic), or (3) from the outside.
From an efficiency standpoint, (1) seems like a bad idea, because it takes heated/cooled living air to vent outside. It also seems potentially unsafe, as it allows an easy path for exhaust to get back in to occupied areas if the exhaust vent has issues. (Not sure what the building codes say.)
Based on your other post, you seem to have (2), which seems to be a pretty good approach. I'm no expert, but the biggest pitfall I see with (2) is that if your attic is too tightly sealed (stuffy), the water heater could potentially not get enough air to breathe. In that case, (3) would be the best approach. But (3) allows uninsulated air into the house, which compromises heating/cooling efficiency.
Basically, I don't think your current setup is particularly inefficient. If you want to make your house more energy efficient, there are probably other things around the house that need more attention (windows, ducts, insulating hot water pipes, etc).
The only potential efficiency problem I can see with your current setup is heated/cooled living air leaking around/under the door into the utility room, and getting "wasted" by the water heater's combustion. You can fix this by making the utility room door seal better. Put something under the door to close off the gap. Weatherstripping in the door frame. Basically, treat it as if it were an exterior door. (Caution: If the air provided by the vent is not sufficient on its own, you may have issues.)
Oh, and since you have at least one gas-burning appliance, make sure you have adequate Carbon Monoxide detectors. They could save your life! You should have one inside the utility room as a first line of defense, and then one in the occupied part of that floor, plus at least one more on each of the other occupied floors of the house (particularly near your bedroom). And remember that they go bad and need to be replaced every few years!