Minerva's Den was definitely worth the price. As for the other DLC's, they're not worth it in my opinion. If you're a completionist and need the DLC achievements or if the DLC is discounted at a reasonable price, then go for it.
thread determines the quality of Minerva's Den.
135/136 games completed (including DLC)
Completion percentage: 99.40%
Latest retail completion: Earth Defense Force IA
Latest arcade completion: Warface