I have an older edition and wouldn't plan without it. As with any guide, be careful of bargains, they may be closeouts ... though only a few trails have changed in the park, the latest edition is nice to have as long as you're buying. No reason not to read the AMC guide, too. In fact, when I go up there I also check the latest reports on VFTT Trail Conditions.
As for maps, maybe they've improved with newer editions of Clarks but the latest AMC map and the Delorme Baxter Park map I think are both better.
Half my fun in the planning and dreaming stage is poring over the guides and maps.