Obviously a car is a great thing to have for many people, if they can afford it, and as incomes have grown more people have found it a worthwhile investment. But a decent, affordable home is a good thing to have too, and I think it's interesting to contrast our enthusiasm as a society for allocating more and more space for cars with our hostility towards allocating more space for people to live in, as well as the very different government policies applied to each case.
Considering how expensive and cramped the housing in much of the country is, you might expect society in general and the various levels of government to be constantly striving to increase the housing stock. But what you actually see is amazingly energetic and committed grass-roots efforts to constrain the growth of the housing stock, which are then reflected in a very restrictive set of government policies. By contrast, people and government in most parts of the country seem united in their determination to increase the amount of car parking available. It's rational for every individual to want cheap parking for themselves, but the aggregate consequences are fairly perverse: you end up creating places like Hungerford and many similar towns around the country, where there are strict controls on using land for anything except car parking, so that car parking is made cheaper and everything else more expensive.
The growing number of cars is using up more of our time as well as more of our space. The more cars there are on the road, the more congestion there is and the more time each car spends sitting in traffic. And because both space and time are strictly finite resources, the opportunity cost of space and time given up to cars is only going to grow if incomes continue rising over time. We seem to be acting with a collective assumption that allocating more and more space to cars is a costless decision, but it really isn't. Over time we have turned many of our streets from places of movement into places for storing large metal boxes - just because the change has happened gradually doesn't mean it doesn't have very important consequences, many of them negative.
In short, I think the growth in the number of cars represents a significant resource problem for our society, one that seems to be receiving roughly zero strategic attention at the moment. What to do about it is an argument for another day: in general I think a combination of supply caps and market pricing would help a lot, but as we haven't even started having a debate about the issue yet any reasonable policies seem a long way off.
Sources for the graph: Private cars licensed from Department for Transport table VEH0103 here, number of dwellings from DCLG table 102 here.