Yes - they should focus more on Prince Harry, how to make money on property in London, new cures for the diseases that come with old age, and stirring up anxiety against immigration. This is what other papers have done and it's been very popular with the masses. Ordinary people aren't interested in the environment, in articles about gardening, or small scale businesses or foreign political activism.
As I've said, the Mirror is a left wing paper which is still successful because it still manages to address the concerns of it's readers and stay relevant to them. This is something that the Guardian used to do waaaay back in the day without reporting on Princess Di or Sam Fox's tits but has lost the ability to do.
I'm slightly perturbed by your claims of what the Guardian apparently doesn't do Mini. The Guardian was the first paper to get in on the making money on property in London schtick and went for the making money in property angle in a huge way right from the start of the bubble. It was totally irrelevant to vast swathes of what should constitute a left wing readership. Ditto it's pages of eye wateringly expensive consumer goods, £15k sofas, £5k coats, £2k dresses. And the food pages! Massively expensive meals with ingredients not available outside zone 2, let alone outside London and definitely not in the north.
Why on earth would people in back to backs with a yard or in flats (y'know, the working classes the left is supposed to appeal to) be interested in gardening articles? Wouldn't they be more relevant to those in big houses with big gardens. Small scale businesses? Yet another area where the Guardian concentrates on places selling expensive impractical mainly unecessary niche goods which will only be purchased by people with quite an excess of disposable cash. And foreign political activism is quite, quite irrelevant to swathes of people who feel unrepresented here but don't really see the likes of Guardianistas caring about that because they're just not trendy or exciting enough for them and they're probably a bit thick and like football or Prince Harry or something.
All the examples you've given are actually examples of their elitism if you dig a bit deeper.
It's a newspaper for very affluent middle class Southerners with lots of disposable cash big houses and gardens.
Perhaps if they actually tapped into things which interested the traditional left wing audience they might have more readers? The Mirror does it, they have lifestyle articles that suggest Morrisons rather than Waitrose and H&M instead of Hobbs.
The Guardian doesn't. And unfortunately if they're going to continue just to concentrate on an ever diminishing crowd of rich publicly funded/third sector/rich retirees in London without facing up to the fact they are becoming irrelevant them you're going to fail.