Having done some very very shit research I came up with the following:
2006/07 our 6 strikers bagged 32 goals (Daal-2, Crawford-3, Lovell-9, Mackie-13, Maguire-1 and Miller-4)
2007/08 our 6 strikers bagged 27 goals (Aluko-3, Brewster-3, Lovell-3, Mackie-2, Maguire-4 and Miller-12)
I don't think European goals are counted in these stats.
Incidently, I think in 2007/08 our midfield got 17 goals with 8 players chipping in (Touzani, Clark, Foster, Nicholson, Severin, Smith, Young and JDV)
If these stats are correct then it would seem that 30 goals from your strike force brings you a fairly average season in terms of convincing victories and real progress. 40 goals would probably feel like a consistently good season. The difference between 2006/07 and 2007/08 looks like a second striker who can pitch in with around 8-10 goals. We missed that last season.