Once upon a time US systems were the best, however seems there are now better systems (for some things) out there and at a fraction of the cost.
Buying overpriced US weapons is just part of the act of homage to the empire. Look at OZ, we used to get great planes from the US, but now we are being ripped off buying the (sometimes) flying lemon F35, why, because we we told we have to.
Why does Thailand need missiles? One would think that under the current climate, the main enemy is the horrible farang, his money, his leasehold of the pool villa, carrying a METV visa and who dares to enter the Kingdom more then x times a year!!!