If you don't get check as promised soon, you can have your lawyer send another time deadline that if not paid within two weeks, the settlement agreement is no longer valid, and you possibly can get out of the settlement and seek other local legal counsel.
Your insurance company might be willing to help you identify the insurance company of the vehicle which struck your vehicle. Once you learn the insurance company, you can turn a claim into them. Suing in small claims court or contacting your Dept of Motor Vehicles could get you to the same...
Diminished value claims really depend on whether you have the right documentation. You will need an "expert" (someone knowledgeable in valuing vehicles) that will have to give you a letter confirming they are an expert and indicating the value of your vehicle, if it had not been wrecked, as...