The Apple Scanner isn't designed as a high-end scanner. It is an attractive, low-cost, entry-level scanner that is ideal for outputting to LaserWriters, using with HyperCard and OCR applications, capturing line art, for "draft" scans to assist in document layout, and so on.
To get the best scanned output from the Linotronic, it is best to use an 8-bit scanner. The disadvantage of 256 grayscale images is the incredible amount of disk space the scanned images consume. An 8- by 10-inch image at 300 dpi with 8 bits per sample, saved without using any compression scheme, consumes upwards of 8MB of disk space. This kind of density also requires a lot of time to scan and print. The average price of an 8-bit scanner is quite a bit more than the Apple Scanner, too!
To support a greater number of grayscales, like 256 on the Apple Scanner would require more than just a new ROM; it is more a limitation of the scanner hardware itself.
The Apple Scanner has been well received by customers and reviewers, but it isn't for everyone. You may be better served by another product.