This is definitely something that is worth spending some time doing right.
However, because it at the end of the project cycle a lot of people put up the bare minimum requirements.
Also, because this will most likely be the first place that people interact with the app, it does not matter how good the app is if the App Store submission leaves a poor impression on the visitor.
It may be apocryphal but apparently Jim Davis, Garfield cartoon strip creator, only spent around 30 minutes a day on his creation and the rest of the day getting it out to the world. This is probably a healthy view to take with anything public-facing – the thing is only a small part, and if making something that resonates with people is a force, the more people that are exposed to the thing is a force-multiplier.
The first thing people will see are the screenshots, and most people won’t “read more“, either the app resonates with them or you’ve lost them.
App-mockup.com is a what I went with for my latest app project, Apt Detector, example bellow.
I used their free option, which was definitely more than what I needed, especially if you use one of their free templates.
To make the App store even happier you can export to different device sizes. 🙂
The slight downside, which could have been my stupidity, is that app-mockup.com exports in .png format and the App Store do not accept anything with transparency. So, after exporting the from app-mockup.com I brought all the images into Photoshop and saved them as JPEGs and making the App store a bit happier.