For MDing, you are not very likely to get silver at any visit. Per year you may get about 20 silvers, or even less (could be more too). The point of MD is that you get quality. You are much more likely to dig a seated that find one CRH. Also, people have even found a few hundred dollars in clad, which can pay off your MD fast. Keep in mind that most silver found CRH is not in circulation from the 1960s and before, it has been replenished by dumped collections. In MDing, there is almost no replenishment. >99% of all MDed silver has been there since the time when silver circulated. The <1% is replenished by either someone's change falling out that contained a silver coin, or a robber losing a few coins from the collection he robbed while fleeing. However, the rate of silver is decreasing in MD as more silver is put out than put in.
I couldn't find a good year report, but just look at this for now:
http://www.treasurenet.com/forums/general-discussion/299944-post-your-mid-year-treasure-report-here.html