Just a thought - docker does have layer re-use to optimize storage in images, at least. In this sense, there is no real storage downside of having rstudio in your images (i.e. you are only storing it once). However, if you are using docker save (yuck!) or something like that, then you are not taking advantage of docker layers.
One big idea of docker is to have ephemeral containers and replaceable images, so that you need not worry about creating lots of images / containers / etc. If storage is your only consideration, then hopefully you should be ok. If there are other things you are concerned about, it may be worth having a wider discussion (new topic) about your general docker architecture / workflow.