I spent 4 months in Maui and have been back a half dozen times. We even got married there
It's one of my favorite places in the entire world!
Here are a couple of my recommendations. the fish market in paia has the best mahi burger on the island. The fish market is near mamas fish house so if it were me I would take one day and head to that area of the island in the early afternoon. Eat at the fish market for lunch (get it to go and walk down to paia bay to eat it on the beach and do some swimming or some bodyboarding if there are waves), then go visit the shops in paia if the wife is into that. When you are done in paia drive up hana highway about 5-10 min to hookipa to watch some of the locals surfing. The waves should be big in the winter so it should be entertaining. Continue about 30 min up the highway to twin falls or look up some lesser known hikes to some waterfalls, then after you have done enough hiking through the jungle head back towards paia, change into some nice clothes, and eat dinner at Mama's fish house. Its another hour drive back to Kaanapali.
Break ins are most common on hana highway so try to pack super light for the day. Dont leave anything in your car that you dont want to get stolen. Its rare, but if its going to happen to you anywhere on the island thats where it will be. Also, its the rainy season in january so the trails will most likely be a bit muddy. Just bring flip flops and shorts that can get a little dirty. Its well worth heading up the highway to the jungle. You wont be disappointed. Its the adventurous part of the island. Below are a couple pics from one of our trips. Im no photographer so dont judge lol.
I'm not an expert on the island but have tried to see as much of it as possible so if you have any questions I would be happy to try and help you out with any questions you might have. Just shoot me a PM.
A little cliff jumping. Most of the time people are nude up there so dont be shocked if you see that on some of the lesser known hikes lol.