Merry Christmas and Happy New Year to everyone. I've been absent from the list for a while, but hopefully back now.
Jim, you pose a valuable question about filters. I always place a filter of high quality on the front of any lens that comes into my hands for use, even rented ones. To protect the front element, but also to have a minor positive affect for outdoor shooting, my filter of choice is always the B+W KR1,5 (Skylight) filter. Equal quality glass/coatings exist in the Heliopan line. And, of course, I don't think you can go wrong with the actual Contax filters, but I don't have those myself. In fact, I even keep a B+W KR1,5 on my yucky old sigma - and I'm sure the quality of the glass of that filter is better than the glass in the lens
Anyway, back to the point. I won't put other brands of filters on the front of a lens because I feel that the glass has to be at least as good as the glass in your lens or you will be degrading your image. (Why pay good money for a good lens to put a sheet of window glass between lens and subject? - a crude comparison, but it makes a point)
If you add a good quality filter, you will NOT degrade the image. You might possible improve it, and you will certainly protect your investment in that expensive lens. (I'd rather damage a filter than front element, wouldn't you?)
If you use a poor quality filter, you will most likely receive lower quality images back than if you used none at all.
The reason I choose a skylight is that I shoot mostly outdoors, and the minor affect is has on haze/light is either positive, or not noticeable.
So, is it like putting plastic seat covers on the new couch? Maybe, but you never know it is there (unlike the covers), it makes no noise when you sit down (unlike the seat covers, don't sit on the filter!) and it actually might improve things a bit (not sure about the seat covers).
Hope that helps! -Lynn