Well, I have been doing other ECs consistently over this whole time... but more recently, I've shifted my focus away from typical "pre-med" stuff. I did my longest clinical experience (2 years at same job) freshman and sophomore year. Since returning to school, I did one other clinical thing (full time for one month this summer) but I started focusing more on other stuff (like athletics, other community service, research). I shifted my focus purposely - thinking that it would be good to round out my application - and because I just wanted to enjoy myself!
In your situation, you have not only two solid years of clinical experience, but also your own personal interctions with the US medical system for a period of time. Provided you plan to mention the latter in your Personal Statement (only for the part it played on your decision to go into medicine), I think you'd be fine with some shadowing over the winter and spring breaks so as to have some recent dates. I do think it's important to have recent dates.