I just came across a PNG optimizer that strips away all the 'useless' information from PNGs. Would it be a good idea to use it on a texture pack to reduce file size or no?
Just don't embed any data to begin with. If the optimizer is making any difference at all then you're adding data you don't need. Look at your image editing software's png metadata fields and make sure they're empty. They probably already are.
If you want to include data in these fields you won't be able to add enough to make a difference anyway.