When I was living in Guatemala, I had a friend from California over, and we decided to go for a road trip from Guatemala City to Acapulco. First of all, we didn't dare to take my old Blazer S10 to Acapulco (wisely so), so we rented a car at one of the airport rentals in Guate City. They told us it was not possible to take a rental car out side Guatemala, but it CAN be done. Just have your credit in order for your credit card, and you're there, with an honest face (and intention), diplomacy, and a good piece of patience.
Driving backroads in Mexico was far worse than driving any road in Guatemala, and both police and military checking posts were frequent between Chiapas and Acapulco. However, the trip is worth every mile of driving, even though it can be hard on the Mexican side to discover the level of service and cleanliness you will find along the road in Guatemala (hotels and gas stations).
Arriving in Acapulco, however, luxury is what it's all about when you get down to the bay. Yet the fish on the beach is expensive, the water is dirty, the shopping experience is what you can expect from any Wal-Mart, and the general price level is high. That was why I preferred the good old ones, and frankly, Hooters in Acapulco was worth every dime both for the service and for the price (and, of course, for the charming girls!) as opposed to the "local" fish restaurant on the beach.
Hotel rooms are generally spacious but marked by time. These are clearly not new developments, but then again, that may be the charm of it. Another hitch about Acapulco is how early everything closes. Even gas stations close around 11pm. It's the curse of having one national chain (PEMEX). I have learned to appreciate the value of Shell, Esso, Texaco, McDonalds (for a safe, early breakfast), Hooters, and TGI Friday's for safe meals and generous opening hours. And cleanliness.
My conclusion is that driving to Acapulco is absolutely worth it (especially if you can watch the cliff divers in action), as long as you have somewhere to drive back to.