Using wonderboard, or concrete board (another brand) really serves many purposes.
For one, it does provide a little extra floor strength, something you donít really seem to need. However, properly bonded to a ĺ" sub-floor, it does take quite a bit of bounce out of it.
Next, it provides what I feel is a superior bonding surface for the tiles, smooth, yet porous. Some will probably disagree.
For another, It provides a water barrier for wet applications such as bathrooms. I donít know what your space will be used as.
Having said that, I should point out that my current home was built probably 40 years before wonderboard was invented. Back then they used diamond lath in a mortar bed, throughout all 4 bathrooms (walls too), and not a tile is loose or cracked. Still, as a policy I try to use wonderboard in my projects, taking into account the change in height of the new floor in relation to doors, trim, etc..
I guess all this doesnít really answer your question, but I hope it does provide information to help ion your decision.