Disagree. Munsters is a great theme, but a crappy game. Same with Led Zep Pro. The Prem/LE are a blast, but way overpriced for what you get. The Pro is so sparse and bare. I would be seriously pissed if I bought those games yet I like both themes. That's a big reason I will never, ever buy a new game without playing it first.
As far as used games go, take a risk. Watch some videos and read reviews. If you think it looks good and you are paying a fair price (you can get most or all of your money back), just buy it and enjoy. I've done that several times. Some games have barely been set up and I realized it's not for me, but no biggie. Other times, the theme has grown on me.