Main Index only shows on the index page. It does not show on other pages at all. You can edit your language file english.php and make the string for main index empty so it does not say main index I suppose.
I know it only says 'Main Index' on the main gallery page, that's why I said I want that PART of the page title, whatever it says, to only show on those other pages, where it is informative. If it shows up on the main gallery page, it is misleading (Main Index sounds like the homepage of the entire website, which the main gallery page is not).
I did what you suggested, only problem being that the dash ( - ) remains after the now blank first part of the title. Is there an easy conditional to use in the template to hide the dash on the main gallery page?