How important is the publication venue for academic hiring and grant applications?
There is probably not a single truth here but I would make the following statements:

Having a good publication record is the basis for basically everything in academia. The question is then what is good? As a fresh PhD student citations will be near zero (I am guessing in most fields). Having publications in citation index listed journals is therefore a definite plus. Having several as first author is a must (see What does first authorship really mean? for a discussion) I would also argue that having papers not part of the PhD (even if not first authored author) is a plus since it indicates activity.

As a new post-graduate you need to improve the publication record as best you can. You need to show that you do your own new work but also be part of collaborations in some mix. Building a publication record takes time and will partly be up to your own efforts and in some way also by chance (you never know what opportunities lie ahead). 

To get employed, you can basically only compete with a good publication list. Everyone knows this takes time and I am guessing all fields have their own "standards" as to what is a reasonable publication rate. In my field where papers are based on field investigations, 2-4 papers per year is considered acceptable, the longer-term average should be towards 3-5. The rate is thus an aspect that should not be over-looked. 

Typically you will have a dip post-PhD because it takes time to build or get into a new environment and to start writing new papers. Having something on the back burner for that period may thus be useful to bridge the gap.

As a final note, the citations will be more and more important after a few years. In my field it usually takes a few years to start getting citations because the results will inspire someone to apply for money, go into the field for new investigations, and then write papers. In a lab or theoretical environment such response times may be lower so check with seniors in your field what applies. A good question to ask is perhaps if there are ways to promote ones work to increase citation records, I do not have the answer to that question.

Bottom line: publish in as good journals as possible. Good quality counts but a reasonable publication rate is also necessary. Citations will come with time.