The point is to have *some* research experience. This can come in many forms: a senior thesis project, a summer job, volunteer or part-time work with a professor, an internship, competitive engineering team. In most cases these experiences are evaluated by the content of reference letters from your supervisors, and if you have them, and tangible evidence of academic output like publications or conference abstracts.
The thing is, the quality of a reference letter is not necessarily going to improve with time alone. If you're in the top 25% of students (but not the top 10%) for one year, doing another year is probably not going to boost you into the top 5%. That will require that you change in a major way.
What you can gain with more time in, or with doing multiple research projects, is the development of skills, and gaining a broader range of experience on which to base your future decisions. With multiple projects you also increase your network a little bit too.
Generally, I wouldn't worry about not having done anything up until now. Lots of people get into great graduate programs with little to no research experience and do just fine.