have a look in one of the tabs, it gives a prestige breakdown (the 4 areas I saw were navy, tech-the probable source of your woes, army and economy). Try to improve these areas. I think military is having a big army mostly, not actually conquering. As for tech trading, it can be downright ridiculous-i offered 'very friendly' GB 3 techs and 40k as the dutch for a single tech, and they refused with 'Knowledge given is not as prized as knowledge earned.' GRAAAGH! Stop saying that!