Well, some people might indeed not care or even like any change.
However, there are certainly groups who will care:
1. Programmers and power users are very likely to care
2. People who are just routinely upgrading to the Fedora/Ubuntu/etc. current release, and thus get new desktop environments as a byproduct, and aren't looking for any change in the UI
It goes without saying, but those are two extremely important classes of users.
> But these must be harmless, easy to implement options (distance between icons, color of elements, etc). What you should not do is to add options which are hard to implement and can destabilize the codebase.
No, what you should do is including useful options and features, especially the ones that everyone else expects to be there because GNOME 2, Windows 7 or Mac OS X have them.
Of course, it all needs to be presented intelligently, and in a way that doesn't force a casual users to configure anything.
In general, simply asking users whether they are power users or not, and which desktop environment they are familiar with should cover a huge amount of ground already.