DMSO can reduce the efficiency of your PCR because it chelates magnesium and so inhibits the polymerase activity. I remember reading somewhere though that as long as you make sure there is more magnesium than DMSO you should be ok.
Personally, unless you are concerned about secondary structure formation causing non-specific amplification (or no amplification), I wouldn't bother with DMSO.
My target gene is has extremely low abundance, but I get an ok yield using seminested PCR without DMSO. That's probably a more time consuming way to increase yield but we are concerned more with fidelity, and the seminested allows us to minimise the number of cycles needed. I guess it depends what you want to use the product for in the end.
Hope this helps