General pricing questions should be on topic
One question we have is How do I find out a fair price for my Magic the Gathering cards?. This question is a general strategy of how to determine the value of card games. Where can I find the value of cards from the Dragon Ball Z Trading Card Game? is similar in this regard.
The key to these is that both questions also have longevity: the answers will likely be valid for years to come.
Questions about a specific price (or "most valuable", etc.) should not be on topic
Other questions are about the specific price of a game:
Any answers to such questions will be relying on price guides or eBay results, and those prices can change drastically over a short period of time.. The price of a card or board game today may not be the same tomorrow.
Say that we had a question asking about the value of the Magic: The Gathering card Tarmogyf. Yesterday, I might have looked up a Magic the Gathering price guide and written an answer saying that the card was worth $257.41. But today, the guide says that it is worth $114.00. My answer is out of date and useless.
The same can happen for board games. Say that game X is the most valuable Avalon Hill board game today. Tomorrow, the game is reprinted and so its value is considerably less. Or perhaps game Y was an obscure game with a limited print run, but the designer hits it big with another game and people are much more interested in his or her earlier game. Now game Y is the most valuable game.
There's also the fact that prices are subjective. If price guide A says that something is worth $100, price guide B says it's worth $200, and there is currently an eBay listing for $300, which one is correct? There is no objective answer and it's up to individual opinion which one is correct.
There used to be a close reason of "Too Localized", which would be an ideal close reason for specific pricing questions. Since we don't have that here, I think that closing as primarily opinion-based would be an appropriate close reason for such specific questions.