I was trying to solve a similar problem and ran into the solution for this and for mine at the same time:
Go to plugins;
Click on “edit” under NextGEN Gallery;
Choose “nextgen-gallery/admin/manage-galleries.php” in the right side list (3rd);
Find “$items_per_page” in the php code;
Set it to be 100 or any number you would like to see…;
Click on “update file” below;
(Should you run into any problems later (which I did not) you can set it back to 25 any time…
