Was the vehicle fully comp insured? If so, then the insurance company should fight for it on your behalf, and in the mean time(like right now) you should have gotten a quote for the damage and then had it assessed and then the assessor should have given you the green light to go and book it in with your insurance company's recommended smash repair place(see if the insurance guarantees the work if you go through a recommended repair place).
Were your wheels listed on the insurance policy? For $1600? I would assume if you yes to both of those, then you should get $1600... not $750. Who offered you $750? The other person or there insurance?? With Fully Comp, they fight it for you, they pay for damage and then they get the money in court later(this is what I would assume). They get the money off the other person's insurance company. But who told you $750, if it was your insurance company, then I would tell them that you insured the wheels and they are worth 1600, provided you let them know of course.
If it was the other person, or the other person's insurance that rang you and told you this, then I would not discuss it and simply give them your insurance claim reference number and tell them to talk to your insurance company, not you, as they should fight it, not you. Provided you are Fully Comp insured.
My car goes in next week, after someone backed into me. So this is where I am getting my info from.