Yes, it definitely is worth it!
Like everyone else is saying... yes it is worth it.
The widescreen capabilities of the HDTV sets almost make it worth it by itself. Also, like Hairsonfire stated, the HDTVs utilize the dvd progressive scanning.
I have an HDTV Ready tv becaus I did not want to spend the extra money to get a built in High Def tuner (cause like you... I will be looking to upgrade down the road). I contacted my cable company and they allowed me to rent a HDTV tuner box from them for no additional charge which is really nice. Overall, I did not see the huge deal in getting the built in tuner yet because in my area there are not that many HD channels. But the ones that are HD, look amazing!