The update manager (possibly combined with the janitor) does a reasonable job of bringing packages up to date with a new release, removing ones that are replaced by different projects etc. However, I'm left with the lingering feeling that quite a few settings are lingering from old releases.

For example, some packages may be left around that I installed myself whereas now the functionality is provided by default. Another example is that my user doesn't get the new theme, and the panel bar is a mess. I can compare against an inactive user on the same system: everything seems tidier. There are also things like the explosion of System Preferences, user groups (inactive user, more recently created, is in groups that the older, active user isn't). In other areas (e.g. default font) I do seem to get given the new defaults.

Another example is Spotlight-equivalent search. I remember Beagle and Tracker, I remember removing tracker when it used all system RAM and swap for 2 entire release cycles, but I don't know what I'm "supposed" to be using now. Is there even a default indexing-search installed and exposed? aptitude install ubuntu-desktop doesn't do anything, so the basics are in place package-wise.

Is there any way to update my settings to the modern "Ubuntu way" without reinstalling from scratch? Can I do so selectively i.e. show the differences?

Most of the time package management on Linux is an absolute joy compared to the alternatives, but if the desktop gets messed up after only a release or two, we're back to reinstalling just like Windows.