My personal rule is not to redeem points for stays of less than four nights, or for room rates under $150 a night. The per-night point cost becomes less (whether you're talking about a package deal or a room-only redemption) for longer stays, so for a short stay, I'd rather save the points and pay outright (which earns even more points for later).
Normally, I'm a penny-pincher anyway, so if I'm paying out of pocket, I'll look for the good room value, which almost always means $150 a night or less, even in major metropolitan areas.
These little rules have helped me save a big pile-o-points while also maximizing the value of the points I actually do redeem. However, as always, YMMV.
