Hi Andrew,
I have done a lot of PDF optimization over the years, therefore, from experience and prior academic knowledge I have to say that what you are asking for might not be possible to accomplish without a significant amount of work.
You can only reduce file size and keep the original quality compacting data through the use of algorithms that eliminate data redundancy, also known as lossless compression. Well, standard PDF files already make use the best compacting algorithms there are.
So you are left with the option of actually losing data usually by downsample or lossy compression which in most cases implies lowering quality.
But since, most times, you only want to keep visual representation of information, you don't care about extra information or how data is embedded in PDF, there are several clever tricks (some extremely time consuming) that significantly reduce file size while maintaining acceptable quality, and that I would like to share with you.