Stash (Bitbucket Server now) lacks a ton of features that Bitbucket (and Github) have. Like most Atlassian products, the base product has subpar functionality that you can theoretically expand with overpriced and/or low-quality plugins.

Also, the degree to which Atlassian products integrate varies a lot. FishEye and Crucible integrate closely. Both of them integrate OK with Jira. Neither of them really integrate at all with Stash, which has its own implementation of code browsing, search, and review. Jira and Stash integrate acceptably, but not very flexibly, and not to a level that surpasses any number of third-party integrations.

And there's no level of integration that would make Confluence worth using.

There is no good reason to be a full-boat Atlassian shop, period. If Jira is what you want, use it; I'm not a huge fan of it conceptually but it there's nothing wrong with it. Crucible is decent if you're willing to put the effort in to get it set up for your workflow. Nothing else of theirs I've used is worth the time it takes to set up, let alone the cost.