+1 for the Nvidia shield, I took the plunge and bought one recently (also have a Roku 4). It most definitely seems to be a case of you get what you pay for. My observations on it are, speed. It's very, very quick. Speed of loading up an Amazon prime show/netflix is incredibly fast, zero lag. No crashes at all. That said, it's also a games machine (which I don't use it for), so it is slightly wasted in the context I use it for, but I highly recommend it. It wiill do what you ask for and the Audio and Video quality is excellent.
Plus if you are happy to go with an Amazon Warehouse deal (i.e. you get a partial guarantee from Amazon, but not the manufacturers deal) you can get one for about £135. Just to clarify I do not work for and am not affiliated to Amazon in any way.