If one wants to generate several papers from a single research project, what is a reasonable way to do so?
There is one trend that I see around me, which is in some cases to split a piece of work in two pieces: a high-impact letter, and follow-up full paper with all the details.

There are many reasons why this might be a good idea. Increase in number of publication is one of them, but there are others:


If you work in a rapidly developing and highly competitive field (i.e. you risk being scooped if you wait 3 more months to publish your idea), this allows you a fast publication of the idea and first results (proof of concept, if you will). Also, letters tend to be reviewed more rapidly, which also decreases publication time. Then, you will publish all the details, influence of method parameters, etc.
If your work would be interesting to a wider community, it allows you to deliver two different messages (or at least, the same message at two different levels) to two communities. This increases the overall impact of your research.