A walnut stock is more difficult to care for ONLY if you overly concerned about scratches and dings. If you have the attitude that scratches, dings, dents, and wear marks are just part of the natural aging process of a working rifle, then a wood stock is not more difficult to care for. You just touch up the marks with a little oil or wax. Hell, people use to use brown shoe polish and it worked ok.
On the other hand, if you are obsessed with keeping the rifle "like new", it can become a hinderance.
It is my opinion that 40 years from now, a 2012 walnut stocked rifle with lots of character marks (dings, dents, etc) will look a lot better, and be more desirable, than a 2012 polymer stocked rifle.