re stucco: I understand that you are not supposed to paint over stucco. If you want to refresh color you need to apply a new layer of stucco. Apparently stucco is supposed to breath or it will rot inside from water damage. Paint seals the stucco.
re roof: even if a roof last longer than 20 years, its still depreciated relative to a new roof. This should be accounted for in the price.
re windows:I would argue that windows is deferred maintenance. A 20 year old window is worth less than a brand new one. Especially if its single pane. Over time, double pane windows lose their seal too.
re kitchen: appliances have useful life. 20 years and you start pushing it. Also, a dated kitchen should be worth less than an updated one. This all costs money and should be accounted for in price. This approach helps when comparing comps too.
re pool: good point, but I included because there are enough 20 year old pools in san diego to make this a relevant question and the cost of updating a dated pool can be quite expensive. I think some people underestimate this If the house you are bidding on does not have a pool, just ignore this particular item.