Well, I think a good tutor can give you many tricks of the trade and facilitate the learning process. That is really the job of an instructor, to make learning easy for you and give you valuable insight.
That being said, the quality of kaplan instructors in my area is really bad. You don't know how many times I have heard of kaplan DAT instructors not even having taken the DAT. Also, coming to class totally unprepared and etc.
But I suppose it varies on the area. Some are probably much better than others.
As for the materials, it isn't anything special really. For the person who wants a comprehensive review of material, the blue book would probably be useful.
Subject tests: The ochem is pretty good. But the biology was atrocious. I thought it was way too easy. Gchem was fairly good and I thought there were some good questions here and there. I think Destroyer gives you a better source/comprehensive base of questions. The solutions are better too in my opinion. In terms of biology/gchem....Destroyer wins hands down. For ochem, both sources are different but good. Destroyer has better ochem solutions though (road maps, more detailed, etc).
The tests: About equal to topscore. The only thing that gets me about the kaplan tests is that they test you only on kaplan material. For actual practice tests, I thought achiever was the best, and a comparison between kaplan tests and achiever isn't even close. Achiever wins this battle by a first round KO in the opening seconds. If you use practice tests wisely, achiever is really all you need for the tests themselves.
For all the additional stuff like flashcards/workbooks: I found it really helpful to make my own flashcards that were tailor made for me. Also, making your own flashcards is a good form of passive review. I had a total of 1500 science flash cards hand made when I studied. If you need extra workbooks for subjects, I think the following are better than kaplan:
Ultimate study guide for Biology (volume I, II, III)
Cliff's AP Biology
Barron's AP Chemistry
Organic Chemistry Odyssey
In conclusion, if you find yourself benefiting from structure, by all means invest in the course. Just be sure to ask ahead and make sure the instructors in your area are good! However, if you are taking the course just to get the material....I think IT IS NOT WORTH 1000+ DOLLARS TO GET THE MATERIAL. By investing around 400 dollars, you can easily get material that blows the kaplan material away!