I wasn't around when the merit system was introduced. But I do know that the forum was filled with spam and garbage posts before the merit system. So to fight this off, theymos implemented the merit system. Correct me if I'm wrong.
You're right, some of us weren't around when all this happened, but we met the story on ground about what led to the introduction of the merit system, i learnt that it was later as well that the altcoins sections was seperated from the other bitcoin discussions section to also confined all those spammers and trollers in the same place.
To be honest, I think merit system made quite the impact to the forum. Mostly to the users. They are trying to improve their post qualities in order to earn merits and rank up. So yes, there were many changes after all.
The merit system has made the quality delivery of members to increase and post what make sense before they can earn merit and that same merit is what will make them rank up, if you're not a spammer indeed then you will concentrate on giving your best in quality post.