You'll enjoy the waterfalls and riverfront in Wailua Homesteads. You might want to make time for a stop at Kadavul Hindu Temple or Kaua'i's Hindu Monastery.
If you're spending some time in Wailua House Lots, Lae Nani Beach and Wailua Beach are top sights worth seeing.
If you're spending some time in Kawaihau, Kealia Forest Reserve and Kapahi Park are top sights worth seeing.