The Tegra 2 lacks good hardware acceleration for 1080p video playback (it's better at 3D than 2D graphics acceleration). That means on some tablets using the built-in player it refuses to play, while on others with a few added by manufacturer codecs (software components that help video playback). There are however several video players on the Android Market that can handle 1080p video. The CPU can handle 1080p standard profile but not high profile MPEG4 H.264 video.
Mobile tech races forward, but tablets honestly have a more leisurely pace. In computers and smartphones, a 6 month old product can seem dated, but tablets make it a year or more. Of course, there will always be something better, but I don't see a radical or sudden leap in 2012 for tablets. Most manufacturers are moving on to different dual core CPUs as I mentioned, and these will hit the market in a few months. Quad cores aren't abounding, but in 2013 may blossom. Right now, Android OS and the apps made for it really don't call for immense processing power and are designed for the Tegra 2 level of CPU.
Is it worth it to buy the latest and greatest? That depends on your budget and whether you're a gadget freak who wants the latest tech. Honestly, we just reviewed the Acer Iconia A200, a 2012 tablet with the same old Tegra 2, and it does everything just fine for only $349 (as long as you don't need 1080p high profile playback or HDMI). It's fine for many folks and gets the job done.
The original Transformer may further drop in price once the Transformer Prime isn't supply constrained. Given Asus' track record for manufacturing tablets (too slow in the first months), the Prime may be constrained so long that the original Transformer stock sells out. Hard to say.