I think you've pretty much got a handle on this. Spanning columns only works in a multi-column frame, not with spearate frames, and muticolumn frames don't yet support uneven widths, so essentially waht you want to do is impossible the way you want to do it.
Chris Z. wrote:
So, I would like to create a grid with two columns of different widths. From what I can tell, the only way to do this is to manually adjust column guides on a master page and then flow in my text.
The only problem is that InDesign creates separate frames for each column instead of a 2-column frame. I can't have any ¶ styles span the columns.
Does anyone have a creative solution for this? I would really prefer not to use separate text frames any time I want to span columns.
Depending on the specific needs of the text flow, you might be able to use some combination of a multiple-column layout, span-column properties, left and right indents, text frame insets, and master-page frames with text wrap properties, so achieve your goal. By "multiple-column layout" I'm thinking of the technique of designing page grids with many columns, and placing page content across one, two, or more columns; in this fantasy, I'm thinking of different span-column properties. For example, with a six-column grid, paragraphs could span one, two, three, four, five or all six, to give the effect of different column widths in the text frame. I've done only the barest minimal experiment; it seems promising. It would take some effort to create, but setting the necessary properties by using styles, the effect could maintain itself without manual intervention, so the development effort would be returned every time you use it.
That's exactly what I ended up doing. It's a good enough work around.