When I was learning classical, I got a 'diamond' nail file from Boots, smoothed the edges of the nail with a bit of really fine (2400) wet & dry paper wrapped over the file and then polished them on a piece of leather! This sounds bizarre but all came as part of a nail care kit from a specialist classical guitar shop in Birmingham. As I say, it's over the top for steel strings, but essential for proper classical playing - otherwise, it sounds too scratchy. I think it's also important to say that nails vary a lot from one person to the next - I am lucky in that mine are quite hard and hard wearing. As you say, a combination of finger and nail is ideal for many players - the fleshy part of the finger makes the stroke and then a release off the nail makes for a nice crisp attack.