I view these things a little differently. It's not about buy/not buy, it's about the right price.
I'll use the now-defunct Fast Forward as an example.
I bought their first few d20 products and was quite disappointed. Most of them were, on the whole, horrid. However, even wading through all the trash, there were some gems to be found - even if it was just in the form of concepts (e.g., Dungeon World).
So, what I did was to set my price. Rather than paying $24.95 for their 128-page books, I decided to set my spend limit at $5 per book. Sure enough, they began appearing on e-bay for $1-5. I snagged several of them for 80%+ off. Thus, they had reached a price point where they were more acceptable. I bought all 4 Demonwars books (MSRP $100) for under $20 (including shipping).