I think one of the big reasons there was no major character development on Smallville was that the writers were kind of wanting to drag it out. Since the concept of the show was Clark becoming Superman, they didn't want to get too close to him reaching that destiny until the very end since in their minds that would mean the end of the show. The same could be said for Lois' journey to becoming a reporter. Unfortunately, this led to some frustration for some fans. Believe me, you are not the only person that feels this way about the show.
In some ways, things did kind of change during the last few seasons, but it was more abrupt and not the slow sort of change that you might expect from a show like this. There are some pros to the last three seasons of Smallville if you are a fan of Lois and Clark. Highlight the following if you don't mind mild spoilers: You do get to see Lois and Clark as reporters, having a relationship, while Clark fights as a prototype version of Superman called the Blur. It's almost like a Superman show without the Superman at this point, and a lot of the teen drama elements do leave in favor of a more traditional superhero show. If that sounds appealing to you, by all means, give the last few seasons a try. Some of the problems you pointed out do disappear from the characters; just don't expect their personalities to go through that drastic of a change.
