I don't know anything about ACARS (there is a wikipedia page on it) but I don't think it has any meaning outside the context of an ops department on the ground somewhere, and some non-cheap airborne kit, which is how airlines use it.
Also, the delivery mechanism can be one of several: satellite (Immarsat in most modern cases, made well known by the Air France crash off Brazil which managed to get 24 messages off before it went down), VHF or possibly even shortwave (HF). I recall one 757 pilot telling me their ACARS came over VHF, so occassionally they would be out of contact. None of these is going to work out cheaper to use or subscribe to than picking up an off the shelf satphone and dialling up the internet with it, and then the world of weather data is your oyster, so to speak
Plus you can do email (if really desperate).
The usefulness of airborne weather data is on
long flights, because it enables a diversion to be made many miles, or hours, before arriving at the planned destination, rather than dialling up the ATIS and having to divert at such a late stage, with minimum fuel. One would find that a 747 from NY is hardly likely to arrive at LHR only to find it fogged in when they call up the ATIS
Having airborne data (even just metars and tafs) gives one a lot of assurance enroute, without having to pester often busy (or only marginally English speaking) ATC.
What one cannot get over the internet is info like an airport being closed due to some drama. I think this does come over ACARS but I haven't got a clue how that kind of info is collected and distributed.
I'd also be happier getting ATC clearances in text form
That's been talked about for about 20 years