A fella at our gym did thai boxing and he couldnt get the stance right for boxing , dead easy to hit. If it was the ONLY option i would go for it but i would always bear in mind it isnt going to cross over, but its a fighting sport and itll be good for your fitness, just remember if and when you go back to boxing you may have to re-learn the technique which depending on how long your thai boxing could take a while!
I've just started Thai boxing after 2 years of boxing (still going boxing btw) and there is not much emphasis on punching or footwork at all as its mainly shin kicks, knees and elbows. I think the main difference is the footwork as you need to be light on your feet to move in boxing but in Thai Boxing your feet are basically set so you have more balance when you kick so anyone that wants to box coming from a thai boxing background would have a lot of trouble landing anything. The thing with going the other way is that when you duck, roll, slip or go to the body, you need to be careful that you don't get grabbed and then proceed to get a knee straight in your face.