Most jobs will actually state that they are looking for a graduate with a 2:1 or higher otherwise you need not apply which is a little harsh I feel considering the level of work that was getting produced by some of the 2:1 students I studied with, and the level of work that I have seen produced by people with no training whatsoever. No amount of kissing up to a lecturer is going to make up for a complete lack of design talent though so even the not so wonderful 2:1 students did show potential or conceptual strengths or something! The same old catch 22 of not having enough experience to land you a job after you graduate is also going to be an issue regardless of your final grade too. I have friends for example who graduated from their degrees 2 years ahead of me, some of which graduated with first class degree's and they are only just beginning to find work that is vaguely related to what they studied. This has of course got something to do with the economy and the job market yes, but it also has a lot to do with a lack of initiative on their parts.
Now what you learn at University on a course like graphic design is far too general to leave you with a concentrated portfolio to help land what will inevitably be some kind of specialist junior position fresh out of uni. Again this is a generalisation as there are some very lucky individuals that do exactly that! I can assure you though, they are few and far between and often happen to have some form of advantage on their sides such as a mentor to guide them throughout their entire studies or influential contacts in the business to land them that crucial foot in the door. Anyway I digress, the thing that is important here is having a good idea of what side of the profession you ultimately want to land up in. This can be a really tricky thing to figure out especially having no experience in the field to measure your thoughts against and most often times this is where the degree part comes in very handy indeed. You effectively get given 3 years of design play time to figure out exactly what you are good at, what you are terrible at, and what you could reasonably swing your portfolio towards once you finally do graduate.
Even still though many do not figure that stuff out even by the time they have graduated because the deadlines are tough and the briefs are not necessarily made up of what you wanted to try your hand at so you can still lose out in that respect. If you are clued in though by some fluke and know exactly what kind of designer you would like to be before you have studied for your degree, then you are in with a good chance of getting a job without the degree. Your portfolio after all will be what sells you not numbers on a piece of paper. It is always good to know that someone has the will power and self-discipline to finish a degree as they are not as much of a ride in the park as they get made out to be, however ultimately an employer wants to know that you are good at what you do.
Im going to defend the degree actually for a moment as I feel that I perhaps have not done it justice. Something that doesn't get mentioned much when talking about design education is your ability to work with others. I remember when I started out on the Multi-Media course at college and at that time I was still fairly precious about any and every piece of work that I did. I always wanted good feedback and if I didn't get it I got a bit upset or despondent and then started to doubt my talents as a designer or creative. What you get whilst at university is forced to show your work to people and have them criticise it. It is something that you get used to very quickly and after a while you wonder what all the fuss was about, and not only that you are having your work criticised by like minded folk who understand the principles of design so you know that the feedback is genuine and constructive. (A little different to asking your nan if she likes the web page you made). This should not be scoffed at as a part of becoming a good designer because it is what will make you a good employee as far as a design firm is concerned. They do not want to have to fight with you on every piece of work you create and expect you to fully co-operate with them and the clients at all times even if it goes against your "design principles". Then there is the fact that you are going to get the chance to mingle with other designers and this will give you a better idea of the level you are working to so the benefits to me are more based in the social part of the degree.
Here are some of the downsides though starting out with my favourite money! Degrees are expensive for everyone, for the rich and for the poor alike. You might be getting a student loan but its not like you wont have to pay it back and that is effectively 20 grands worth of debt you are volunteering yourself for there. Aside form that there are things to consider like computing costs, printing costs, software costs, outside training costs like internships and drawing classes, none of these are free. You will end up spending a lot of money on a degree and there really isn't much of a way around that so get used to the idea of being broke. It hardly seems worth it when you add that to the amount of time it will take you to get work that is relevant to your studies and that will most likely be an entry level job at an entry level wage. This is why I actually feel that you may well be better off doing job specific qualifications as and when you need them to suit the particular faction you lean towards. For example if you are leaning towards being a photography lead designer for a fashion magazine then get a job doing something run of the mill to pay your bills. Do an evening course in photography and volunteer one day a week at a fashion house and I wouldn't be surprised if you found yourself a quicker route into the industry that way. You might also have a lot less debt to be following you around too. Another thing is that the library is your friend! with access to the internet via your phone, in internet cafes, and in most peoples homes, there really is no excuse to not having access to information. You can find reading lists for degree courses on there websites and simply go to the library and read them yourself for nothing. this way you can give yourself a good education without spending thousands of pounds to pay the lecturers wages. Do not underestimate the power of books. I think it was Will Smith who put it across the best in saying that "the key to a good life is running and reading". If you read there is not one problem that somebody else hasn't already had so they might have a good answer for your situation too.
Anyway in answer to the question posed in the title, a graphic design education should consist of what you need it to in order to get your foot in the door. There are too many variables when it comes to peoples lives, level of skill access to resources etc for me to make an honest judgement on what a design education "should" look like, so I am going to have to give you one of those wishy washy not really an answer type conclusions in the this post. It should be the means to an end and those ends should keep changing and growing with your career.