I dunno, while an old guidebook can be fine for maps and maybe general descriptions of places, it can be hit or miss with just about anything else. Tourist sights can close for refurbishment or be renovated in such a way to be totally different. Hotels and restaurants can close, be remodeled, change in various ways. Transportation options can come and go.

You could probably start with an old guidebook then supplement it with web research for the details once you're looking at places to see, stay, eat, whatever. But even the general feel of some places can change if the guidebook is several years old. Personally, I don't find the amount of money saved on an old guidebook to be worth it. I'd rather have the latest one, and also I like to glance through several different guidebook publishers to see which one appeals most, which means going to a large bookstore for the best selection.

Having a recent guidebook on a road trip through Northern California and Oregon last summer helped us pick places to stay (both planned ahead and unplanned) and places to eat, as well as what to see. Our favorite guides right now are Moon Handbooks and Insiders' Guide's "Off the Beaten Path" series, but there's still a lot of personal preference in the choice of which publisher.