Don't forget GP2 brought us Lewis Hamilton. F3000 was a bit of a dud, that is true. But there is a consistent pattern that the most solid drivers tend to have had notable success in F3000 (eg. Heidfeld, Alonso). I think F3000 and GP2 are series where the money factor has over-riding influence on driver performance, in contrast to F3 where drivers in mid-field cars can still score good points.
British F3 is past its use-by date. Its level of competition has dropped lot in the past decade. It hasn't brought forward any particularly shining talent into F1 in recent years. F3 Euroseries has done much better with Hamilton, Kubica, Vettel, to name a few.
Really, the only ones worth seriously considering are F3 Euroseries, GP2, and WSBR. A1GP tends to attract promising drivers, but the level of competition is so erratic, it's hard to judge them. IRL is predominantly oval racing, so that's another hard one (although very respectable).