You didn't ask, but here's my opinion: Trying to do non-standard things to save space is a recipe for problems later on. Will every device you want to play your songs on support mono? Probably not.
This reminds me of VBR encoding in MP3s. Seemed like a great idea to save space at the time. It turns out to cause no end to problems with various systems (especially when used in a video container). Now that hard drives are so much bigger, it seems like a silly solution.
Right now, I think disk space is so cheap that everything audio should be ripped at full, lossless, original format. In a few years, the disk space will be even bigger and cheaper.
Again, just my opinion.
Brian.
