What is the best justification for applying for a multiple entry retirement visa in Thailand?

The only multiple entry retirement visa is the Non-OA visa. This one requires a many things including insurance, but you don't have to transfer money to a Thai bank account in order to maximize the time in Thailand.

Most people get a 90 day non-O visa, which is single entry. You enter Thailand and the visa is "used" and then you have 90 days permission to stay in Thailand. You need to open a bank account and put 800,000 baht into the account within 30 days of your arrival, so you can apply for a 1-year extension after the money has been in your account for 2 months.

A multiple-entry visa means you can enter unlimited number of times until the visa expires.

A re-entry permit makes your permission to stay not be discarded when you leave the country, and you can return with the same stamp you had when you left. You do not get any additional time as the days of your entry stamp continue to tick down while you're outside the country.