I totally agree with you, Pink Duck, that everyone should use JOSMs built in validation before they actually upload any changes. This I always do myself before I apply chanegs.

But for correcting other peoples mistakes from the past, that probably didn't know how to validate or didn't use one, Keep Right! is one good system that I will keep on using when I have the spare time to sit with it.

Here's a few other ideas on what I use.
highway=path for ways that are not pawed, but rather paths in what used to be grass. Around areas and houses and things like that.
For grass areas I use landuse=meadow. But it could be out of place for you here since you have trees to?

Will this mean that the maps will be rendered faster, will the OSM Database be easier to access. What will it mean?