FYI, if you are looking to exchange in, the hotel-branded resorts are going to be a much more difficult exchange if you don't own one of their resorts, because they all have an internal exchange program that you will be competing with.
If you've stayed in Wailea, you should understand that Wailea is the Beverly Hills of Maui; you are not going to find that "luxury" feeling in either Kihei or Ka'anapali. Kihei is the most affordable area in West or South Maui, so if you're used to Wailea, it might be quite a culture shock for you. Kihei reminds me of Myrtle Beach or Destin, FL. You won't be seeing any celebrities staying in Kihei, but if you want to get a cup of coffee, it's not going to cost you $10 either. The beaches along this stretch are universally nice, though getting into the water can vary from easy to difficult based on the lava rocks. Kihei is probably the best location if you plan on exploring Maui. It's certainly the most centrally located.
IMO, Ka'anapali is a step up from Kihei and a step down from Wailea, in terms of "luxury" and price. It's more like a nice suburb on a beautiful beach. Most of the Ka'anapali timeshares are right on the beach, whereas most Kihei timeshares are across the street from the beach. While the hotel branded resorts will be a difficult exchange, non-branded resorts will be much easier IME.
I'd personally rank the beaches in this order: Ka'anapali, Wailea, then Kihei. I also found Wailea to be much windier than the other two resort areas.
Another area to consider is Napili. It's farther north than Ka'anapali, so definitely farther off the beaten path, but I'd personally stay there over Kihei.