My efficiencies were very variable to start with - buying crushed pale malt in 25Kg bags, first bag had good efficiency, second bag was terrible, third was back to pretty good. But it became noticeable that the first brew from a bag had much much better efficiency than the later ones, so obviously the crushed grain was just going stale and losing it's enzymes.
Then I made a mistake with my order and got whole grain instead of crushed. It may seem a bit illogical but I bought a grain mill (even though the grain mill cost more than the 25Kg of grain!) so I could use the stuff. It's one of those little hand opperated ones like a big mincer and was about ��ã40 if I remember correctly. My efficiencies went through the roof. Also my final gravities dropped from about 1014-1015 down to 1010 and depending on the yeast even 1008. So I'm never going back to crushed grain. These days I'm using about 8Lb of pale malt to get the same OG as when the recipe calls for 10 or more. So I now get 7 brews from a 25Kg bag rather than the 5 that I used to get.
Even with this little grinder I find that I can grind all the malt in the same time my boiler takes to get the water up to mash temperature so it doesn't add to the length of the brew day - though it takes 110 turns of the handle to grind 1Lb of grain...