I value my time above everything else (you can always make more money, you can't add years back on), and so I always look at the value of what I'm spending vs. what I'm getting in terms of entertainment. For example, going to the theater is about $30 per person at a nice theater and with a drink/snack. $30 for a couple hours of entertainment. It's passive entertainment though, so I value it lower than active entertainment (such as, say, bowling, pinball, gambling, etc). If I feel my time was worth what paid, then I have no issues with spending the money. Realistically, the longer you own a pin, the less it has "cost" you (in terms of entertainment value). If you trade or sell, sure, you may be cutting into that entertainment value, but it really depends on the difference between pin A (which you are trading/selling) and pin B (which you are trading for/buying with the money from pin A).

Anyone who plans on owning and enjoying pins for more than just a couple years is going to get their money's worth in terms of entertainment value. What do you value your time at?