I haven't been in a couple years, but last time I went the backlot tour was so reduced that it hardly seemed worth the wait in line. Ever since they put in LMA, it seems the only thing the backlot tour has going for it is catastrophe canyon (or whatever that part with the special effects is called). Has it changed?
You can see the best HS has to offer IMHO in a half day. For me that would include TSM, RNR, TOT, Muppets, Great Movie Ride, and Star Tours. If you do this half day plan though, you'll be a bit rushed and likely miss some good shows (Beauty and the Beast, Indiana Jones)