[TMWNN]

You're saying that Spain wants Gibraltar back because it wants to liberate the benighted residents of the rock, which of course isn't true. Spain might claim as such as part of its overall case for regaining the territory, but that's certainly not the main, secondary, or tertiary reason.

If Sardinia were not an island hundreds of miles away, but a large peninsula physically connected to Spain, yes Spain would very much actively try to regain the territory. (Probably much more of a priority than Gibraltar.)