I agree, I don't think with 1.6 rockers you will gain any bottom end, if anything it will add a small amount of hp, but the stock cam is so weak I doubt it would be much.
Spend the money elsewhere. Good long tube headers might add a little bottom end... Igntion will give a better throttle response, more crisp, but I doubt will add any more torque. The stock 318 is mostly built for low end so improving it can be pretty challenging.
A good intake will go a long way, IMO the LD4B is a little more HP oriented than what you are going for, I have one and the runners seem pretty big for a 318. I have a Offy dual port and have run it and that thing is torque monster and good to ~5500. Don't know anything about the Weiand, other than looked into it and bought a LD4B... haha