I have a few comments. First off, why would you need o quick working to get an MBA? Or a CS master's for that matter? Both my wife and I have spent most of teh last 20 years going to school while working full time. And full time often means 5-60 hours a week. I had a period about 5 years ago when I was a senior executive - I worked 7 days a week for almost 3 months, 60-80 hours a week. I traveled extensively during that time AND I completed most of a master's degree during that 2 year period. I have since done an MBA in finance and I can tell you that the MBA is a cinch in comparison. Nearly everyone in my MBA program wa working full time.
With a low key, 35 hour a week job I know the only thing keeping you from getting a master's degree is yourself. Most "good" schools offer executive MBA programs. I think Stanford has an online or distance CS program. If they don't there are many other good schools that. If it is something you want to do then do it!
Second, if you are happy what you are doing then you should place a lot of value on that. Would doubling your salary and working twice as much increase your happiness? It might, I'm just saying that is a question to ask yourself. At 23 you have a lot of time ahead of you. You are doing well to have a job you like. And if you really want to keep monving up then by all means, keep going to school. I see nothing wrong with taking a few years "off" working for teh publisher and getting a little experience while you decide what you want to do. But if your salary is so low that you have trouble getting by then it would be counterproductive.