Nicator wrote: What does Macedonia's wealth have to do with it? These power broker types are international types, perhaps, Persians, Athenians, Lydians, etc...
Don't forget that Macedonia was on the forefront of world affairs for some time. And with the centralized political structure and key strategic location north of Athens and between Greece proper and Persia, Macedon was well positioned to take full advantage of manpower, resources, and trade. And for Demosthenes to focus his rants on Philip with such a rabid intensity, Macedon must have been more than just a backwater 3rd world horse depot. And big money is almost always in the know where opportunity exists and can be exploited. And then, as now, these power brokers would not want to be known or recognized. That would invite thieves and other forms of financial attack. The speculation can go no further. But it is that speculation where big money types have pulled some strings and set up an assassination that is the point here. Beyond that, why bother.
Still trying to understand who these unrecognized "big money" types are supposed to be, especially during the pre-Hellenistic period. In Greece there were cities, farms, and monarchies, and it's self evident where the money came and went as far as the monarchies are concerned. Farmers sold to the city. The cities took care of their own - the more money a citizen had, the greater the amount he had to contribute to the pool, so would have been impossible to hide one's wealth. Major commodities were slaves and grain, and when grain had to be imported (frequently) the prices at the source were known. There was no opportunity for middle men type traders to both grow rich and to hide that fact.
The same goes pretty much for cities outside of Greece, and we pretty much know how Persian wealth was distributed. I truly doubt there was opportunity for great money (and therefore power) to be "hidden" there either.
You've said the the speculation can go no further, but I don't think it's gone far enough unless you can suggest in more detail who these "hidden" big money types might possibly be - within the context of the period - and how they believed they would benefit by "exploiting an opportunity" such as having Philip assassinated.
You don't have to convince me of anything, of course. I'm simply letting you know where I'm stuck regarding this hypothesis.
Best regards,