These projects and the changing Google logo can be thought of as marketing expenses to maintain Google's brand, which helps them continue to attract users and d

These projects and the changing Google logo can be thought of as marketing expenses to maintain Google's brand, which helps them continue to attract users and developers. G+ is built for strategic reasons (and not something they're just doing because they don't know have 'enough useful ideas'.) You can debate whether G+ is the right thing for them to do, but they're building it because Google leadership thinks they should.