DH mapped the walk from LM bldg 8 to main building; it's roughly half a mile. So, not a huge amount but yes, it can feel like it's much longer at the end of the day.
I didn't mind the walk (we were there for 9 days in April) and the LM area was actually pretty quiet and not overly hectic as many describe the value resorts.
Also, in regard to landscaping, I found it to be one of my favorite details about AoA, particularly the walk to/from LM. There were 3 distinct areas while walking from the main bldg to LM; ocean for Nemo, savanna for LK (complete with piped-in 'bug' sounds!) and then great "underwater" landscaping for LM. (My only note for improvement: Better lighting along the walkways or at least signs for folks to watch out for lizards and, especially at night, the little frogs!)
We actually enjoyed the resort so much in April that we're headed back in December for 13 days. We're having to do a split stay between POR and AoA because AoA didn't have availability for the whole trip.
(Side note: We're two adults, no kids, and request a king bed LM room)