I don't think it's a bad idea to have it respawn weekly or bi-weekly, even monthly wouldn't be terrible. I really see nothing negative about it other than if people want to try and get better Snorlax's or making up for an "accidental" crit. Yes once breeding gets implemented it won't matter as much but it's an alternative to breeding at the very least and might make people log on who might not have originally just to try and get a better Snorlax. So no its not a necessary feature but I do think it'd be neat