I don't think Pompey as destroyed much, the Seleukid kingdom was nothing than the shade of a glorious past, when he came.

Now, for my responses:

A better and stronger government, more easy to say than to do...
In my mind, the real weakness was this constant focus on Antioch, I think that a Seleukid king staying at Seleuki, in Babylonia, would have been in a better situation.
As long as AS have hold this region, their economy was strong.
The eastern regions were not SO important, and could be abandonned to Baktria and Parthia, but Babylonia and Elam, along with Media, should have been kept no matter the cost.
They failed.

Of course, every empire crumbled, without strong armies, economies and without a sentiment of unity by his own subjects, he couldn't stand.

Seleukids kings have also rellay bad luck, getting the Romans on the head just when they have finished Carthage...bad idea...very bad...

At last, empires and country are absolutly not the same thing.
England and France ( and Belgium, Germany, Spain, Italy... ) are not the same thing that theirs colonial empires.

And...I absolutly not understand the intervention of sir Edward on this subject... military defeats and political changes_even civil wars_ doesn't indicate that this country doesn't exist.
The US have done more than 40 amendments to their constitution in their short existence, is it not the same thing that changing the constitution ?

The political system of the United Kingdoms in 1900 wasn't even democratic, and became only a few years after...so the England of queen Victoria is not the same country than the England of the Beattles ? :]