Its up to you but you may be asked about your exit out of Thailand by the airline you fly with. I have been asked before and told them I hadnt chosen a leaving date and have always been OK
If it concerns you, buy a bus ticket to Laos for a few quid and simply show them that.
I qualify for the retirement but would probably go on the DTV as I dont receive state pension and would like the security of being able to earn an income
It depends on what you want your lifestyle to be in Thailand. If you're going to lay by a pool by day and prop bars up by night, go for the retirement
If you're going to be busy, taking breaks outside Thailand and want the freedom to earn, opt for the DTV.