I think it depends where you want to end up in single seaters. There are two different career paths.
I won't comment too much on US racing as my knowledge is stretched, but for example if F1 is your goal, then Atlantics, to me, are a waste of time, but essential if you're going to go for Indy Cars.
In terms of importance it's hard to verify - there are so many 'new' series that it's difficult to determine how important they are until they have been around a few years.
Here is how I see the motorsport ladder at the moment, in Europe:
----------F1----------
----------GP2----------
--Formula Renault 3.5/Superleague--
F2
F3/GP3
--Formula Renault 2.0--
Formula Renault BARC
Formula Ford/Intersteps/FBMW/
|