Thank you all for your replies.
In my 35mm days, all my lenses had a Skylight or UV filter as a matter of course. I had Hoya filters on all my lenses. With Digital, I read that new cameras already compensate for UV light, so the purpose for that filter disappears. I read recently that camera retail shops will push filters for protection as they have a high profit margin on these items. It's why I'm not automatically going for filters this time around.
For landscapes, I live on an island, so will often be by the sea & for macro, I could be spraying a flower with water to get light through the droplets. This means that the lens could get fine spray on it which would mix with any fine dust particles & need it to be cleaned. Any night shots I take are most likely to be night skies.
It is easier to clean the convex surface of a lens than a filter, but it's less stressful cleaning a filter surface as it is much less expensive if damaged. I'm very careful with my equipment, so scratching is unlikely, although not impossible. I'd have thought that an impact would be just as likely as a scratch & a filter would be unlikely to help in an impact.
Regarding quality, I think that any additional item in front of the image will have an effect, but Hoya or Nikon is going to be good glass & I would tend to believe that it's much cheaper to build an optically good piece of flat glass, than it is to build a lens element.
The only quality issue I feel is ghosting when taking against a bright light source.
Reading back, I may have talked myself into filters for protection, but I have already changed my mind twice while writing this.