Depends really. Blu-ray won't be disappearing any time soon - there'll be sufficient demand for a disc based medium for at least the next few years (in the UK at any rate). Also, once you buy a Blu-ray disc, it doesn't disappear. So as long as you have a Blu-ray player available, you can always watch that disc. In that sense, "investing" in Blu-ray discs isn't really that risky (after all, I am still able to play all my DVDs and even VHS tapes today if I really wanted to).
There's also no chance of getting the kind of picture or sound quality that you can get from Blu-ray through a streaming solution any time soon - so some films will definitely benefit from being played on Blu-ray. But having streaming solutions will certainly augment any home movie collection, since it gives you instant access to any film offered by that service (though be warned, Netflix's choice is apparently fairly limited at the moment, so shop around and use free trials where available).