I'll argue that going digital is amazingly valuable toward improving your skills relative to using film. Back in high school, I was the head newspaper and yearbook photographer. I shot, developed, and printed an awful lot of film. I learned a lot about photography, but I felt that going digital really took things to another level for myself.

When you go digital, you can take advantage of instant, immediate feedback that's just not available with film. Most notably, you can leverage the histogram feature to recognize when the automatic metering blew it and you can compensate in the field. Contrast that with the old-school technique of shot bracketing (and burning a whole lot of film). Likewise, you can shoot so many more variants on a shot, giving you a better chance of getting good results. Two hours of careful darkroom work maps to about five minutes of Photoshop tweaking. Digital is just a huge win all around, particularly if you assign a dollar value to your time.

If I was going to go back and shoot film, it would have to be large format view camera. That gives you sharp resolution and perspective control you'll never get with a digital camera any time in the immediate future (or, at least, at a price point you could afford).