apart from Imageworks I also created ImgOrganizer a while ago and put it on Openrepos. While it may not be the fastest, it offers to create albums. By long-pressing an album (or folder), you can now batch-resize all images. Same goes for multi-selected images: after selecting multiple images in an album, long-press on any image and select RESIZE, then chose either height or width and it will be scaled up proportionally.
And last but not least, if you open an image in full-screen mode, there are a some editing tools like RESIZE available, too.