Question: Buying the game...

[Naria]

If you don't purchase Heavenward then you will still have access to all of ARR's content, just none of Heavensward's. General quality of life updates (such as changes to the user interface) you will still probably get, but as the ARR updates will end when Heavenward comes out you won't have access most of the updates going forward.

That said, there is a lot of content in ARR (also called 2.0), and you probably won't even be affected by anything in Heavenward until you reach level 50. If you are not sure if you are want to commit the money then I'd wait on purchasing Heavensward until you are closer to lvl 50.

Heavensward is FFXIV first expansion as ARR was more of a reboot than an expansion. If they continue on the same pattern then expansions will come out every 1.5 to 2 years. Keep in mind you also get large content updates about every three months, with minor updates in between, as part of purchasing the expansion.

Edit:
I am also pessimistic on how long SE will continue to support the PS3 version as Heavensward is the only expansion that they have defiantly said will be supported. It could go either way for future expansions. While the PS2 was supported for a long time for XI, it also ended up hindering XI's development. The director/producer Yoshida has said that continuing to support the PS3 after Heavensward will depend on the size PS3 playerbase and how constrained the team feels by the PS3's hardware. PC will be supported for the life of the game .