The media is expensive, of course, but the ultimate question is will you even use it often enough to justify buying it?
If you will, then sure, I suppose that it's worth it, but if you'll hardly ever burn Blu-Ray's and just want to watch them, then just get a normal Blu-Ray drive (although it may actually be easier and more cost effective to get a writer anyway).
Edit: I see that you will be using it, and for backup's, yeah, it's a good investment.