What is your Blueray player? If it is an older player, it may be limited to 1080P. If you are sticking with the Elite Plasma, you won't get the benefit of a 4K Blueray player, but if you decide to upgrade to a 75+ inch TV you will. Getting an external streamer is a no-brainer though. Content is king. Online streaming services have so much readily available content if you are so moved. No need to even lock into a single service. You can buy a month a time and flip around between services.
With the new compression CODECs and the relative high bandwidth for HD streaming, up to 2-3 megabytes per hour, the quality is very good. You don't need to spend much money either. Google 4K Chromecast, Amazon 4K Firestick, ROKU 4K all support the popular streaming services, Netflix, Amazon, DisneyHD, Paramount, etc.