Here are some simple scripts to extract the exif focal length data from your storage directories and calculate some statistics. From that point of view You might be able to decide what focal length do you need to strengthen...

first: extract exif headers (linux or cygwin, jhead needed) (stores in file /tmp/foc):

find . -name "IMG*.JPG" -exec jhead {} \; ~grep Focal ~tee /tmp/foc 

then this calculates the stats (perl, parameter: /tmp/foc) 

sub perc 
return (int($_[0] / $db * 10000)/100)."%"; 

while ($sor=) 
$sor=~ s/[^0-9]*([0-9\.]+)mm.*/\1/g; 
$sor=~ s/\n//g; 
if ($sor>0) 
if ($sor<=35) {$below35++;} 
if ($sor>=70) {$above70++;} 
if (($sor>=35) && ($sor<=80)) {$betw++; $avgb+=$sor;} 
if (($sor>=45) && ($sor<=55)) {$betw2++; $avgb2+=$sor;} 
if ($sor==35) {$e35++;} 
if ($sor==75) {$e75++;} 
if ($sor==80) {$e80++;} 
if ($sor==300) {$e300++;} 
print "rows: $db \n below or eq 35mm: $below35 (".perc($below35).") \n"; 
print "above or eq 70mm: $above70 (".perc($above70).") \n"; 
print "35-80mm: $betw (".perc($betw).") (avg:$avgb) \n"; 
print "45-55mm: $betw2 (".perc($betw2).") \n"; 
print "35mm: $e35 (".perc($e35).") \n"; 
print "75mm: $e75 (".perc($e75).") \n"; 
print "80mm: $e80 (".perc($e80).") \n"; 
print "300mm: $e300 (".perc($e300).") \n"; 
print "average: $avg mm \n"; 

example results: 

rows: 1930 
below 35mm: 0 (0%) 
above 70mm: 704 (36.47%) 
35-80mm: 506 (26.21%) (avg:54.37) 
45-55mm: 84 (4.35%) 
35mm: 804 (41.65%) 
75mm: 34 (1.76%) 
80mm: 464 (24.04%) 
300mm: 89 (4.61%) 
average: 69.3533678756477 mm