Hi Erin - sorry things did not work out as you had hoped. This is one of the challenges of professional wedding photography..... thinking on your feet, dealing with the unexpected, being able to improvise with little or no time.
I won't belabor the obvious, but either you should have scoped the place out in advance, or carried enough "light" with you to deal with any situation. I also echo PCUNITE's comments.... we see a lot of that here. Many here in fact do shoot available light, beautifully, and we thoroughly enjoy examples they post. But there are extremely dark reception halls and other places beyond our control from a lighting standpoint, and at those times we need some help.
You mentioned horribly grainy low light images - sounds like you did not have a tripod either which would have saved a number of shots. Coming from a studio background I'm a little bit surprised you made no mention of this tool...... you do have tripods in your studio? It wouldn't have solved all your problems, but for decades I shot dark churches at ISO 160 and 400 and got beautiful images at slow shutter speeds.
But to be constructive - if you seriously want to go this route, you need to purchase powerful external flash units, and solid power to drive them....either good rechargeables or power packs. As others have pointed out, you need to "think tight and crop" when dealing with ugly venues. Concentrate on faces and really narrow your framing for the action.
Often the ugliest venues have some area of plain wall or background. Crop tight using these and it will help things. Post some samples though - perhaps things are not as bad as you think.