Honestly, I'm gonna have to put this out here: the sprite font plugin as it is, quite honestly, quite tedious to work with in order to get the bitmap font set up in the first place. It mainly has to do with how the sprite font files are formatted.
Nobody makes sprite fonts in a uniform grid. No-one at all. And quite frankly, there's a good reason they don't. There are already standard formats for bitmap/sprite fonts, one notable one being Angelcode's Bitmap Font Generator format, .fnt, which is supported by multiple notable engines already, and it can also be generated in an XML format. ShoeBox can also generate bitmap font files for fonts hand-made in image programs, as well, and can also generate it in XML.
And then there's some bitmap fonts out there that use the format used by the Bitmap Font Writer.
I really do think sprite fonts are great, but the problem is, the way the plugin is set up right now just makes it far too tedious to actually set up a sprite font properly, especially with the knowledge that there are far easier methods of achieving the same result.