Should I attend a conference even if I don't have a paper accepted there
I work in computational condensed matter and have attended both computational (or theoretical) and experimental-oriented conferences. When you submit an abstract for a conference in this field it usually does not imply that you are committing to publish that work in the conference proceedings or that you thereby refrain from publishing that work in a journal. Top conferences (in this field) will encourage and give you the chance of publishing in their proceedings, but will not require it.

What usually happens, is that if you can get the paper published in a reputable research journal you do that, and either 1) choose not to submit a proceedings paper or, the option that I find most interesting, 2) submit related technical work that, while still sound and rigorous, might not get published in a journal but will get accepted as a conference proceedings paper.