Google works on PageRank which is a type of link popularity. It does almost no good to be listed in DMOZ as the PageRank of the pages you are on are so far down that it doesn't matter much.
It does help for theming.
Almost all my traffic comes from Google. I am #1 on Google for teen sex, lesbian sex, porno, asian porn, sex stories, and a bunch of others. I know that lots of people believe what you have said, but it is a common misconception. People think the same thing about Yahoo. It doesn't hurt, but it won't help you much either. Trust me - I know Google like the back of my hand. I always try for a DMOZ listing, but if I don't get it - it won't matter much.
I know what you mean about the alphabetical categories - you are right for the categories themselves, but most people use the search. For SEO purposes - it is better to be listed on a page with LESS listings. This is because the "points" you get are the "points" of that page divided by the number of links on that page. That is a slight over simplification, but that is the way it works more or less.
If you want to see HOW MANY google points you have - you can use the google toolbar:
http://toolbar.google.com/
for more Google info - you can check out my page at:
http://www.searchnerd.com/pagerank/
If you look at the Adult Categories in DMOZ - you will see most of them are worthless - same with Yahoo. At least DMOZ doesn't cost $600
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