Pinging sites like Yahoo every half-hour for several days or weeks, to notify of updates when they haven't been made, does nothing but clog up the system. It's called spam-pinging and it has been around since 2002.
If you haven't updated your blog, or you're pinging updates of a site that isn't even a blog (or RSS feed, where applicable), in the long run it's just going to make it harder to get listed at these sites.
In the short run, you could get yourself banned from sites like Yahoo, though it isn't officially their policy to drop sites for spam-pinging.
There is an ethical way to get into search engines and achieve high rankings with a blog, but it's not a matter of volume. It's more a matter of timing, supply and demand. But explaining that process takes a level of detail and an amount of space not available here.