How relevant are (journal) papers for the valuation of one’s work and results?
How much people rely on your publication record to judge you depends on how much they understand your research.  The further they are removed from your area of study, the more they will depend on "the numbers".  People who work in your subfield will base their opinion on the actual quality of your work and on your reputation in the community.  Fortunately, the most important evaluations (i.e., reference letters) usually come from people in your subfield.
Not all publications are created equal.  Let's say I'm hiring a postdoc.  Candidate A has 10 publications with almost identical titles all in low-quality journals.  Candidate B has one publication that describes a significant breakthrough and is published in a good journal (I don't mean Nature or Science, just a journal that is widely read by people in the field; e.g. (in my field) SINUM or SISC).  Who would I hire?  Almost certainly candidate B.  Indeed, Candidate A's publication record may actually be a negative factor.
Publications matter most in academia.  A mathematician friend of mine took a job at Google after graduation.  They didn't really care about his publication record; they hired him because he had created the Cython language, which was purely incidental to his research.  If you go the academic route, your publications will be a critical factor in your evaluation for getting a post-doc, a tenure-track job, and tenure.  If you go to industry, they may not matter so much.
Publishing norms vary by field.  In mathematics, for instance, people may sit on a result for years while they refine it or try to develop it further.  Senior people may just put their papers on the arXiv.  In other fields, it seems like new developments must be published within a week, and you're expected to write vast numbers of papers each year.