Why would it inhibit economic developement? Thai Rak Thai was instituting nationalist economic policies like limiting foreign ownership even more than in the past, and they had even frozen the construction of new foriegn-owned corporate retail such as Carrefour, Big-C, Tescos, and 7-11 due to the complaints of local retailers. I doubt that a democracy ruled by the masses of rural poor is going to produce a governmental environment more pleasing to multinationals than a military dictatorship answerable to a monied elite.
Well it would inhibit economic development because of the lack of political stability that is brought on by a military coup and dictatorial government as a whole. While the last year or so in Thailand has been anything but stable it still had an elected government and it seemed as if most of the problems would be solved in the upcoming election. Democracy plus the promise of more stability within the democratic system usually puts investors on a better track. Military takeovers usually show to the international business community the lack of respect for law and protocol as well as the underlying fragility of democratic institutions. Also with a military coup the rule by fiat can be quite detrimental to the health of foreign investment. It is much easier for a dictator to nationalise all foreign owned industry than a democratically elected leader.
Also, whatever you say opebo, Thaksin never took measures that the Junta is now taking. He didn't ban opposition parties or ban protests by those who opposed him. He was ruthless, cunning, and despicable but he was hardly the autocrat that the Generals seem to be.