OK, I think I see what you did.
You don't have a double spread layout, you have two single (opposing) pages that are text pages.
In the group of text pages there is no double spread. Double spread layouts are only in the group named "Two-Page Spreads"'
You say "both pages are outlined with the yellow border so I assumed they were going to be treated as one page". This assumption is not correct. You can click on one page and then Ctrl / Cmd - click on the second page and both pages are selected, and both pages are outlined in yellow. But that doesn't make them a Double-Spread layout.
So in short, with text page layouts you cannot achieve the design that you want.
The only work-around that I see is the solution that you already tried:
Select a Double-Spread layout and use the <Page Caption> box for your text.
You say "Spacing lines of text vertically with these caption options so that I can put a title, author and publisher separated with a lot of white space, is quite a cumbersome procedure".
I agree, it is. But it can be done.
The caption box will expand as you add more text or add more (empty) lines wiht <Enter>. This will put empty vertical space between your text lines. You probably know that already.
You can move the text on the page using the "Padding" feature. This feature will add blank space either all around, or on select sides only. By selecting "Padding" for one side only you can move the text acroos the page horizontally or vertically.
Well, it ain't Adobe In Design - but it's doable. After all you have only one or two title pages.
