Hi tcat007,
I think of everything in terms of tradeoffs rather than “defeating the benefits” of something. If the benefits of the mattress pad (some extra surface softness at a very low cost but using lower quality synthetic materials) are more important than the benefits of the wool quilted cover you have then it would be worth it.
The Dreamaway has a fairly thick layer of polyester fiber (the down alternative) which would add some surface softness to your mattress but it also would reduce the ability of the wool to regulate temperature and would probably sleep a little warmer. Some people would have no problem with this while others may notice it. Polyester fiber will also compress and become firmer as it packs down over time.
Are you looking to “fine tune” your mattress by adding some surface softness or pressure point relief to your mattress (which would be the most common reason to add a mattress pad instead of a mattress protector)?
You can also read a little more about different types of mattress pads in post #10 here.
Phoenix