I like this page to visualize what a bunch of pennies looks like: http://www.kokogiak.com/megapenny/four.asp 30,000 pennies is less than one cubic foot. This image comes from the above link and shows almost 50,000 pennies.
I'd never get tired looking through wheats I bought from a noncollector. Who knows what you could find? However, I don't do much roll searching anymore, so I guess I understand. I got a small jar with 1-2 thousand. Kinda cool to look at. There are many from each decade, but I think I took out any coin worth more than a dollar
I have so many that my trailer house sunk in the ground. I can only get out the back door anymore. It does make security a little better.
I put those in 2x2 holders. I got a binder going and have most of the dates and mint marks. Then I have a metal box holding the duplicates.
I don't have the keys, like the 1914 d or 1931 s, and of course the 1909 s vdb. But I got just about most other semi-keys. However, the more valuable or lower mintage ones I have are in lower circulated grades. I got so many sets going its hard to really work on one. And I collect mainly world coins. For instance, I got British large cents going, Canadian nickels 1920s-1950, FAO coins, etc. it's fun, to say the least
1909 VDB, 1910-s, 1911-D, 1912 s, 1913 s, 1914 s, 1915 s, 1922 d, 1924-s, 1924 d, 1926 s. Those are the main ones I think of as semi- keys.
Jez, I honestly don't know! If you add in my memorial cents, I venture to say 50,000+.....too many. I spent the last few years paring it down by selling spares. I still have many I want to sell.