The RL while being a great car is simply not strong enough to steal customers from other brands. It's a combination of things really, most major being:

1) The RL is built much better than E class, 5 series, GS and M, it feels like a tank and has a better paint job besides maybe GS. However its styling is too bland it doesnt quite catch the eye.

2) It uses much better materials and hardware, and has a lot more gadgets than GS and M, but it doesn't look as rich, it look futuristicly boring, just doesn't have that sense of luxury. It also doesn't have a brand image of BMW to be able to get away with that.

3) It's engine isn't much better than M35 or even Avalon and upcoming Camry. Yeah, BMW can sell the 525 with less than 200hp for almost the same money as the RL, but Acura simply doesnt have the brand image.

4) No flexibility. There are people who could live without AWD and avi and half of other electronic gadgets to save a few bucks. And quite frankly, people that have 50k to drop on a car, probably can afford to drop a few more grand on a v8 variant. People that are buying V6 variants of cars are value buyers, and its necessary to provide them with options.

So basically, while the RL is a better car than most of cars it competes with but it simply doesn't appeal to many people. In order to steal customer that are willing to shell out 50k for a car, they need to do everything better - more HP, better styling, better interior and less money. Just look and the Infiniti M - it's simply destroying it's competition. More HP than any car in its class (besides of course the RL which has a bit more than M35, but that will probably change soon), awesome styling, gorgeous interior and so many options to chose from.

Right now the strongest selling point for RL is AWD, but M35x is stealing most of it's potential customers, and the upcoming GS350-AWD with much more competitive engine than current GS300 will make the situation even worse for RL.

If Acura isn't planning to discontinue the RL all together, they must take immediate measures to save the sinking ship. First and most of all, they need to offer options, and have base version start at $42k at most. Second, they need to do something about exterior styling, make it more agressive, and perhaps offer more colors. And then they need to go back to their roots, and make the engine the most powerful in class. It doesn't have to be a V8, but if it's gonna be a 3.5L V6, it needs to slap silly every other 3.5L V6 in its class, and perhaps match the power output of competition's V8's, like Honda used to do particularly with previous gen TL-S and NSX. Right now Honda is getting beat at their own game with Infiniti and Lexus technically ahead of them, and MB and BMW breathing down their neck.

And did I mention they need to resurrect the Legend name?