If you are pretty upset with the fact that you were mis-sold, don't worry too much as you could just make a call to Dell and ask for a replacement. I have seen that some people were lucky to have their replacement but some were not as lucky - Dell customer service turned them down for a replacement unit. I believe that best thing to do is to make an order of your laptop through the telephone as a representative will be able to answer all your questions prior to you making an order.
I have posted an article with regard to the non 3D screen, i.e. 900p resolution here. The only concern with the non 3D screen is that you will not be able to upgrade your XPS 17 (L702X) to 16GB as you would only have 2 memory slots. The only way for you to received 4 memory slots would be to get a 3D screen + 3GB GT555M 3D capable gpu card.
Well, you could ask me whether it is worth while ordering a 3D screen as compared to a non-3D screen, Before I answer this question, it is important to look at the pros and cons about having a non-3D screen and having a 3D screen.
If you have a non-3D screen, you would have the ability to use Nvidia's Optimus technology. Basically, it switches automatically between the integrated graphics and the Nvidia GT555M gpu card. In doing so, you would have around 6-8 hours of battery life with a single charge. It also depends on your workload for the day. Compare it to you ordering a 3D screen + 3D capable Nvidia gpu card. If you have ordered a 3D screen + 3D capable gpu card, you will be able to experience fully 3D movies and games (where available) on your XPS 17. The downside to it is that Nvidia Optimus is disabled.
What it means is that you will have the 3GB Nvidia GT555M gpu card always switched on. That would translate to a 2-3 hours of battery life on a single charge as compared to the 6-8 hours of battery life if Nvidia's Optimus technology is enabled. I just don't understand why Dell would want to disable Nvidia's Optimus technology. That would be a shame. The good point of hacing a 3D screen + 3D gpu card is that you will have the option to upgrade your system memory to a full 16GB instead of the 8GB on other configurations.