I think mainly it depends on where your interests are. However, I'm willing to bet that 3-4 years actual experience at development has already taught you more than any 4-year computer science degree ever can. I have seen some of the recent output from C.S. departments, and frankly, it is appalling. If you are interested in a degree simply for "practical reasons" (IE. just to get a job), I would focus elsewhere.
A lot of this depends on the type of company you might want to work for, and even what sort of industry. Also, a lot of this is social/culturally decided, rather than based on merit.
Fortune 500 companies that are not directly in the computer industry tend not to like taking chances. They like to either get fresh young graduates, and train them in their company culture, policies, etc..., or get experienced people from similar industries, with established credentials.
Internet/computer companies tend to be a little more interested in your actual performance than in your formal credentials. Companies that are developing radical new ideas, or new startups, etc... tend to fall in this category, as well as smaller tech-savvy companies. Generally, I have found that the more tech-savvy the company, the less they are interested in your credentials, and the more in your actual experience, ideas, and abilities. One company I worked at had two C.S. graduates, and two programmers without C.S. degrees (I am one of the latter). Which two programmers ran the shop? You guessed it; the two without C.S. degrees. In fact, I have no formal certification in any computer field, and I _always_ have work. At the moment I am freelancing in web app development, while considering two possible job offers.
However, it's not bad to have
some sort of University degree, if you want to be a more well-rounded person. And this tends to help when moving up in the corporate world in general. I have no C.S. degree, but I have a degree in English, and I took several courses in scattered areas such as Calculus, technical writing, programming, and foreign languages. I don't regret this, but honestly I have learned far more about any of these areas by self-directed study than any University course.
If you're interest is just in getting a job in the near future, then I recommend you simply work hard, and dig into the books to prove you can learn. Don't focus on certification, but on developing unique applications that prove you are capable of independent though. For example, while working your full-time job, freelance at developing special applications for smaller companies, or even open-source projects that prove your abilities. If you really want to go to college, I would recommend you take a range of courses (like the classic "liberal studies" concept), because this will open your mind and give you better communication skills, and understanding of the world in general. Of course, if you want to be a researcher/theoretician, that is another matter, but you will need more than 4 years of colledge for that, and a mathematics degree would probably be better preparation.
Think about it this way: the world has plenty of 4-year C.S. "duh-velopers", but what would companies give for an experienced programmer who can write well, or who understands economics, etc... The biggest problem in the modern IT world is not what the programmers are capable of, but how to actually make the programming have value to the company. This requires just as much knowledge of people and the world in general as it does specialized computer skills. -------------------
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