Not only can you now legally drive/ride in the Kingdom of Thailand, your licence will also act as legal identity if you get stopped by Plod (by law you must carry your passport with you at all times) and you will also get the Thai rate for entering museums and shows, which can be a substantial saving.
You can also use it for domestic travel which avoid needing to take your passport.
Best of all if you were to get nicked for a driving offence you will still be able to take to the road as you have a second licence.
Cost of all of this was THB 2 300 for the Proof of Residency at the UK Embassy, THB 100 for the med cert, THB 105 for the bike licence and THB 205 for the car licence (last two are vague guesses as we paid the agency THB 2 500/person for taking car of things for us). Both licences are valid for two years and on renewing next time you get a five year deal.