Someone might be a newbie in the forum but his/her knowledge can't be. They can be good knowledged in cryptocurrency than most of the senior/hero/legendary members of the forum. Wouldn’t that hurt the newbie if they are restricted?
Spam isn’t only done by newbie. Most campaigns require x amount of posts which indirectly are responsible for the spam.
I think current system is good but being a little more harsh on moderating or increasing the stuff would be good idea to prevent the spam.
Also, see what theymos think about newbie jail.