Assume you have the 3/4 MOA gun, is it going to be more productive to try to get it down to a 3/8 MOA rifle and then go practice in the field or start practicing in the field right away? If you have have unlimited resources and unlimited time, of course it would be better to get the rifle as accurate as possible. If not you need to be efficient with your resources, otherwise there is a good possibility you are going to end up with a rifle you can shoot really good off the bench but not in the field.
My way of thinking is if you can't shoot small under controlled conditions off the bench, which is where you learn basic shooting skills, then you don't have the skills to make long field shots. You need to learn trigger control, breathing, sight picture and wind until they become natural and 2nd nature to the shooter. Maybe, just maybe, that 3/4" gun is really a 1/2" or 3/8" gun in the hands of another shooter. How many times on here have you seen someone with a rifle accuracy problem, and someone recommends having someone else shoot the rifle?
Have you ever been to the range with a buddy, and one or the other consistently out shoots the other with the same rifle and ammo? To me, working up a more accurate load adds to trigger time, concentration and muscle memory, not to mention reloading skills. Once you have the rifle shooting to it's full potential, then I would say go practice under field conditions. That way the shooter knows for certain that a bad shot(s) is more than likely his skills and not the equipment and can concentrate on developing his skills and technique in the field.
Any sport costs money. It also requires time and dedication to become proficient at whatever you do. If you can afford a new set of golf clubs but can't afford any balls to hit or have the time to go hit them, you're in the wrong sport. If you can afford a new fishing rod, but not fishing line or a lure or bait, you're in the wrong sport. If you can afford a drag race car and not the fuel to race it, you're in the wrong sport. If you can afford a long-range rifle and not a scope or ammo to shoot it....guess what!
An inaccurate long-range rifle doesn't teach you anything except that you can't hit what you want consistently.
If you can't shoot it accurately off the bench, going to field conditions won't all of the sudden make it better. In actuality, it makes it much worse. Don't fool yourself into thinking it won't.
You said it yourself...."of course it would be better to get the rifle as accurate as possible."