I think we're at the point (628) where going through each one (with only 10 listed per screen) is more than a bit tedious). If they could all be grouped by TYPE on a single screen and multiple items (or Select All) could be applied, I think that would be TREMENDOUSLY helpful.
The in-game OXZ Manager has only 474 at last count. Where do you see 628? The filter feature in the OXZ Manager (press 'k') lets you filter by categories, tags, etc. The only benefit I see in a multi-select feature would be when you want to install many OXPs at once with an automated download queue instead of having to start each download manually. It is rare to be installing many OXPs at once, so this would be a niche feature.