I bought a Tiffen UV filter to go on my XA10 to protect the lens. I am going to buy the Canon WD-H58W wide angle for the camera. Does that render my Tiffen superfluous when I am using the wide angle? Is there any reason to keep it on and put the wide angle on over it? Moreover, is it possible to put a polarizer over the wide angle to protect it? From the photos it appears the answer is no.....

Yes, you will not need or want the UV filter when using the wide lens. I don't believe the lens you are buying has filter threads, so no, I don't think you can use a filter on the lens, but I could be wrong.

I agree. If the UV is there to protect the XA10 lens, you do not need it with the WD mounted.

If you need filters with the WD (no filter threads as I understand it) consider clamp-on holders. The Cokin system with the universal ring might work (but I've not tried it).

I've got Canon WD-H72/43 wide angle convertors on all my A1, A1S and HV20 and HV40 cameras, obviously I think they're great, I don't take them off :)

What first impressed me was the great colours through them. Those bigger lens are heavy on the front of your cam,
so you'll need to re-balance it on your tripod.

I have a thin strip of white adhesive tape on the lower left side of my A1/S cams and I balanced the camera with the heavy WD-H72 lens
on it, on my tripod. Then I marked the corresponding position on that tape, so I can quickly set the rig up.

Correct, they don't have a front thread for filters, but they could have provision for a lens hood. I've made cardboard hoods for the A1/S cams
but wind can be a problem.

It seems to me the front glass has a tough protective coating, but I'm always careful and use a blower brush to remove sticky airborne microgrit
before I run the cleaning cloth. Always do this at home before you go outdoors, by then it's too late :(

Cheers.