They don't work nearly as well as advertised.

Does anything work as well as advertised? Anecdotally, I've seen most people who try it getting some sort of improvement, and orders of magnitude improvement is not uncommon. Unless you've tried it yourself, or have friends who have, or have some empirical evidence, then I don't know where this claim comes from. Even if this improvement doesn't quite measure up to some of the more sleazy marketing materials, it can still be substantially better for some guys than any other alternative currently available.

They don't work as well as going to the gym a few times a week.

Evidence or reasoning, please.

They have low information density. If you chose to study just the works of David DeAngelo, that would be about (I'm guessing, but not wildly) 25 hours of DVDs and 60 hours of audio, plus another 200 hours of recommended readings, not counting practice and review.

This one is correct. You have to filter through this stuff and figure out what applies to you, how to become an intelligent consumer, and how to throw out what you regard as incompatible with your ethics or personality. Low information density is unfortunate, but it will have to be dealt with by those who don't have better options.

You would probably be better off taking that time and learning how to dance, play an instrument, or speak a foreign language.

What evidence do you have for this claim? Anecdotally, there are many men who do these things but still lack success. For me, being multi-talented got me some attention, yet that attention was useless when I couldn't capitalize on it.

The advice you are giving is pretty much conventional wisdom. If I had followed it years ago, I suspect I would still be more-or-less at where I was then. Instead, I have wildly more success than back then, and I've seen other guys accomplish the same thing. Consequently, I hope you are not merely repeating conventional wisdom and that you have some additional evidence or arguments for the claims of this post; otherwise, the overconfidence displayed might lead others astray.