An obsolete chip will tend to be worth more than face value if:

1) It has a denomination of $5 or less.
2) The rack was destroyed when the chips were taken out of play
3) The chip is from a desirable casino
4) The chip is from a desirable location
5) The chip is attractive
6) The chip is in good condition

And when you add all these factors together, the result is that a chip, obsolete or not, will be worth more than face value if demand is greater than supply.