For the pair I think the opening bid is reasonable. Is it high? Sure, but not unreasonable. The two pages together tell a story, and that always adds value. A stand-alone illustration is a pretty desirable thing, since you can frame it and stick it on your wall and a lot of people who see it will say, "Oh, Bukowski!"
I'm not sure you can compare illustrations with paintings, since the paintings aren't as characteristic as the drawings (fewer people would look at one of his paintings and say, "Oh, Bukowski!"). I suspect that the average Bukowski collector would prefer an illustration to a painting for that reason. I don't know.
Value is fluid, but if the statistics on bukowski.net are any indication, his popularity among young people is steadily increasing. In 10 years many of those young people will be working jobs that provide them with disposable income, and I think when that happens you are going to see the prices for the manuscripts and art - which have been pretty static for the past decade - rise.