I think the Beatles were always good song writers but I actually don't think they made any really important music until their psychedelic days. Sgt. Pepper is almost definitely the most important thing they ever did, so I would say that when they started introducing a lot of the psychedelic stuff their popularity wained because a lot of the people that listened to them just wanted that pop sound and didn't want to think and they were the same people who where against the counter culture that was influencing the Beatles to expand and actually try to do something with their music. So those people got pissed, but a lot of people started listening at that point too.

Anyways.

getting back to the topic. Straight forward lyrics are fine if thats what you like. It's more about figuring out how you write and create and getting yourself in a position to best do that. It doesn't matter what your doing, like i said if you do it well (communicate well) then someone will notice, the number of people that will notice just depends on what your doing and how relevant it is.