they have tightened up since exemptions were introduced, I know many folks who have been challenged incl my wife who made two trips back to SIN(her home) whilst renewing her retirement visa, both times she was questioned regarding her intentions - after explaining she was admitted - not sensible to encourage people to game the system can have serious and expensive consequences but ETA will put an end to all these debates thankfully.
The fact that you have already had a retirement visa will be a red flag you have already demonstrated that you are not a genuine tourist, first time you will be questioned about your intentions thereafter you may be denied entry or at least given a final warning and flagged on system……better to just legitimize your status,
the many spoil it for the few, the warnings are out there now, folks should heed - the ETA can’t come soon enough and that will put a stop to the systemic abuse of Thai hospitality. Try getting into AU/NZ/US without correct visa……