Something that hasn't been mentioned thus far but I think bears mentioning about (3): If you rely on flat files to store data, then you've got to worry about file locking; that is, two CGI processes fighting over or otherwise munging a flat file in a very bad way because each doesn't know the other is doing something to the data.

Frankly, it's easier just to learn about how to put together a simple database than to deal with all the issues that arise from working from flat files. (By easier, I mean maybe not to get the thing running at first depending on your level of familiarity with databases, but over the life of the project, in terms of maintenance and upgrades etc., the time savings will be considerable.)

I'll reiterate what the earlier poster said for emphasis: Only good things will come of learning SQL and some basic database skills. You'll use them over and over (and over and over ...) again in your career. Furthermore, with the advent of high-quality open source databases (I have used MySQL quite extensively for things that don't require the big iron approach of Oracle and am very impressed), your learning curve is not very steep, the learning environment is free and very easy to install (based on my experience with Linux), and the production environment is super-cheap (assuming you're a good citizen and donate a few hundred bucks to the open source group :-).

Hope this helps!