These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Linda and Heather (a show that exists within the universe that's only ever heard, particularly the theme song) appears to be an in-universe expy for Liv & Maddie itself. Doubles as an In-Joke or Shout-Out likely to the male Periphery Demographic that exists for this show (as it was introduced for a plot point revolving around Parker being a fan of the show).
Certainly a Shout-Out, given that two of the show's writers are the team of Linda Mathious and Heather McGillvray.
Some Anvils Need to Be Dropped: Special mention goes to the episode Rate-a-Rooney. This episode addressed a rather important issue about girls and their self-image.
Squick: Joey unintentionally hits on Liv ("Kang-A-Rooney") in season 1 and Karen ("Pottery-A-Rooney" and "Kathy Kan-A-Rooney" - yes, twice) in season 2. The guy has the worst luck.