It's difficult to discern the difference between 720p and 1080p on a 50 inch screen for the vast, vast majority of eyes (especially taking into account the "average consumer,") if you think consumer home devices with "ultra HD" resolution are anywhere on the horizon you just don't know much about HT in general. Why? It would be outrageously expensive for the consumer, it would be outrageously expensive for the manufacturer (in addition to providing no real visual benefit,) 720p, 1080i, and 1080p have already cemented themselves as “the” HD formats for consumer HD material (1080i and sometimes 720p for broadcast and 1080p home video,) broadcasters would NEVER be able to provide the bandwidth for resolutions that immense, and you wouldn't see a damn bit of difference on most for-use-in-home screens between the HD now and the “ultra crazy stuff” you're talking about. On a spec sheet the differences appear to be gigantic, in practice that could not be further from the truth.
Extremely large movie theater screens are a different story.
So “is it worth it” to buy into HD right now [for use in the home]?
Yes, yes it is..... because nothing you're talking about will have an impact on home theater in the next handful decades (if ever.)