Skripal poisoning, cui bono?

As a foreword, I'd like to say that, on a personal level, I remain convinced of Putin's involvement in the attempted assassination of Russian ex-spy, Sergei Skripal, in England.
What I want to focus on in this post, however, is the quite fascinating spectacle that is occurring right now in British and American media surrounding this event.

Firstly, it's worth noting that the amount of media attention this case has gathered seems to me, without exaggeration, ridiculous. Sergei Skripal was a double agent, convicted in Russia for treason, but subsequently released. Already at the moment of his arrest, he didn't anymore present much value as intelligence asset for neither Russia, nor the UK. On a surface level, his attempted assassination would seem to be an affair internal to the Russian secret service. Why are the USA and UK so concerned then, if he had already expired his use as a spy?

No doubt there is more to the whole issue than we are being told by the British government and media...
In his article, Craig Murray, former British ambassador to Uzbekistan, presents a few alternate scenarios, different from those promoted by the English press, which he (rightfully) says are equally as probable and legitimate as the current official narrative. In his words, he "witnessed personally... the willingness of the UK and US security services to accept and validate intelligence they knew to be false in order to pursue their policy objectives". This certainly lends credence to his way of thinking. Although I personally remain unconvinced of Putin's innocence, I definitely agree that US and UK "intelligence" tends to work their investigations "in reverse": first proposing a convenient theory, then looking to validate it. (We need only remember "pulling babies out of incubators", Assad's non-existent sarin, or even fire- and explosion-resistant Saudi passports)

In the end, why is the English-speaking media so caught up in Russia's blockbuster-like spy-drama?
Surely, both the US and UK have enough domestic problems of their own for the press to report? Is it possible that some Russian intrigue is merely a good enough distraction, to divert the public's attention from more pressing issues?
We can outright exclude the UK security agencies' concern for their citizen. If such were the case, the dialogue would be centred about the improvement of measures to prevent the import of dangerous substances, or possible travel restrictions. Instead, we are presented by the media with a variety of methods completely unrelated to English domestic security to directly attack Russian political, diplomatic, economic and military interests in their own home....
Why should the United Kingdom mobilise their entire military and intelligence capabilities, only to get petty "revenge" for a foreign ex-spy? (without sufficient or even adequate proof, no less)

It's starting to look increasingly like the UK government and their media lackeys are simply looking for excuses to beat the drums of war, no matter how ridiculous the premise.
What the people of England and America have to ask themselves, is this: regardless of whether or not Putin actually killed his own spy, do we really think that's a good enough reason to throw away our daily routine and prepare for a tit-for-tat (possibly nuclear) confrontation with one of earth's strongest armies? Do we want to risk any goodwill that we have left with the Russian people and Russian business, and instigate the largest global conflict since WW2?

From the Russian side, we see warm gestures, despite UK rejection. It's now up to the western governments and people to decide whether they want to reciprocate the partnership and work towards a constructive relationship, or possibly plunge the world into a nuclear catastrophe from which our planet's ecosystem will not recover until the end of days...