The highways that loop around both the West Maui Mountains and Haleakala are both in poor condition, but can be driven in a standard sedan, four wheel drive is not necessary. However, your rental contract may prohibit driving around the backside of Haleakala (and some also prohibit driving the West Maui Mountain road). This prohibition stems mostly from the cost or in some cases the refusal by tow trucks to service those remote areas.
Both of these roads are simply roads, without any major points of interest, mostly just a way to go all the way around the island. All of the main island POIs can be reached by sticking with the other roads (perhaps an out 'n back such as the Hana Highway).
A couple of driving tips from a former kama'aina ... When descending from Haleakala shift your transmission into lower gears to slow the car, don't ride the brakes all the way down. Too many Maui rentals have warped rotors from being overheated while descending the mountain ... When driving the Hana Highway, pull off when you have a couple of cars behind you and let them pass you by. Nothing more frustrating to locals than being stuck in a group of six cars behind a tourist driving at 15 mph, and the Hana Highway has very few places to pass safely. Don't be pilikia, let em by.