The 100% width worked right away when I tested it, so your are calling the correct css class.
You will also have to remove the borders form the headers, rows and cells, so add th, tr, and td to your css, like this:
.dokuwiki table.inline {width: 100% !important;}
.dokuwiki table.inline, .dokuwiki table.inline tr, .dokuwiki table.inline th, .dokuwiki table.inline td {
border: 0px !important;
}
You might also want to consider using the Wrap Plugin, this way you can create different table styles.