I think its value was largely technical; Akkadian had served the same purpose, as an international language of diplomacy, administration, and commerce, for a millennium or more, but Aramaic was superior for two reasons:
- Akkadian was on its way out (as its speakers were shifting to Aramaic);
- It is easier to train a scribe to write in Aramaic, due to the facility of the script and its grammar (at least compared to Akkadian).
Remove the technical advantage represented by the script, and the Achaemenids really have no reason to adopt Aramaic; in fact, on the basis of prestige alone, Akkadian would probably hobble along in its role as
lingua franca, despite the fact that most of its speakers had moved on, just as Latin did in Europe.
The most interesting result, from my perspective, would be to see SWEurope united under a kind of republic of letters by means of the cuneiform script (as "the cuneiform world"), just as East Asia was for a time united by the Chinese script, and for much the same reason: you can theoretically adapt the cuneiform script to represent new languages, such as Aramaic and Arabic, and they will be more or less comprehensible to anyone who reads the script. Already, most Semitic languages are no more distant from one another, linguistically speaking, than the Chinese dialects (with languages like Persian serving as an analogue to, say, Japanese or Vietnamese). Consequently, you could have another millennium or more of people speaking these languages but writing in "Akkadian" (just as they did for the previous millennium, writing what is often called Peripheral Akkadian or as my mentor Huehnergard sometimes jokingly called it, "bad Akkadian").