TThis is by far the best answer to the question. The legal answer. Others may have experienced different situation but as Stuart says, do not be the one who is caught out.
Depends in all circumstances, on the police involved and on the insurance company. My point is to always be aware of the rules and of your insurance policy.
There is no such thing as a valid International Driving Licence. If the Thai police stop you, you will need to show them your national drivers licence which is valid for 90 days in Thailand. If your National Drivers Licence is not in English the Police will want to se your International Drivers Permit which really just translates ypour national licence into English. In any event, the Thai police may want to see your Internationa Drivers Permit due to their incomplete training and understanding. After you have been in Thailand for 90 days you are expected to have a Thai licence. Your vehicle insurance probably requires that you have an In International Drivers Permit (or after 90 days, a Thai licence). Very easy to get could out by invalidating your insurance and can also be extremely expensive if you badly injure or kill someone.
Not lenghty but more hoops to jump through. Photos. visit to you home by immigration, drae your house map, more paperwork, wife must go to immigration when you apply. May more questions from immigration. If you have the funds then entension of stay based on Retirement (you have an extension rather than a retirement visa) is much, much easier.