I can't possibly see how they should be included in net worth. A more interesting thought exercise would be to come up with ways of monetizing them besides saving on travel that one would otherwise not pay for, meaning you actually spend more money using them (fuel surcharges, meals and ground transport) than if you didn't have them, because you'd be too frugal to foot the bill.
Examples of ways to monetize huge points surpluses:
1) if they're redeemable for hotel points, spend a month living in a hotel, especially if you're transitioning between rented apartments, as opposed to paying rent.
2) offer to book flights for friends or coworkers using your points and have them reimburse you for part of it. E.G. book $600 ticket value and ask for $300-450. They get a discount, you get cash for extra points you don't have time or energy to use.
3) if points are eligible to use on rental cars, go carless and rent one on an as-needed basis.
Any other ideas? This way, you may not count points in your net worth, but you can use them to save money, increasing your net worth. Using them for taking trips you aren't forced to take doesn't save money, it just gets you a really inexpensive trip. That still decreases your net worth, even if it's only by fuel surcharges and dining out in another city.