We've recently had a flurry of questions regarding alerts and availability and dampening. Search this forum on that topic to read some background. You might find some suggestions to help.
In short, today's availability alerts are triggers on the availability state changes - "Going" DOWN and "Going" UP. So you only get alerted when a resource's state changes - if its DOWN for 1 day, you will only get the one alert when it initially went down.
I think Joe on a previous forum thread talks about this and possible solutions enhancements. There may even be a JIRA on this.
mazz is right, we've lately seen many requests asking for similar solutions. the forums should have plenty of good, recent information on alerting and dampening, especially as it pertains to availability reporting.
on the other hand, what you ask about sounds a little like batch notifications, which is slightly outside the bounds of what dampening is intended to do. whereas dampening is good for reducing notifications based on occurrence / frequency of some condition in the system, batching is good for consolidating disparate notifications.
when i think of batching, i'm reminded of the options you have when you register to some forum. you can choose to get a separate email for each and every post to the forum, or you can get a daily digest. the daily digest would be equivalent to a batch every 24 hrs. i'm thinking that this same principle might be useful for alerting. instead of receiving alerts immediately, they would be delayed and aggregated. i'm thinking an option as simple as "one email very X minutes/hours" might do the trick.
however, even if this feature is implemented, you'd want to carefully consider the consequences of turning it on -- although it cuts down on email, a very important alert notification may get delayed for quite a while before it's delivered.