By changing it to character level you will be effectively giving the players 30 bonus Rep per level, and remove the utility of abilities like the Noble specialities Noble Blood. I use a number of different tracks, representing standing within subgroups as well as general recognition for players actions. I've also been known to hand out Renown directly for player actions.
I have considered the "free Reputation" angle, and I would certainly take that into account when tweaking the system. I am more interested in what effects Renown has actually had in folks' campaigns.
The way I plan to use it is as the actual representation of the character's reputation in the world. If they don't have any renown, no one knows them. Simple as that. People might know of the characters
exploits, but not the characters themselves (i.e. "The dragon has been slain!" vs. "[PC Name] slayed the dragon!").
I also have it that the characters won't be able to purchase certain types of renown unless it makes sense. Noble renown won't be available for purchase until they've
at least actually talked to someone of recognized nobility (otherwise you have titles coming out of nowhere) and likely until they've actually been given a title as a reward.
But anyway, renown means actual recognition. If they don't get any, they'll never be seen as more than a bunch of nobodies by society at large.
So would you get rep for doing things in a particular way? Such as having a big announcement in the town square before each "adventure" so if you succeed, there would be "witnesses"? Just curious. Seems with this reasoning, a PR guy would give bonus rep!
I can understand targeted rep depending on the actions done to gain the rep (and in some cases "counter" rep with any rival factions). Could cause headaches for intergroup relations if there are differing rep trees explored (say between the Assassin and the Priest, by a certain level, their social pressures of "Why are you hanging out with
him could be a problem, depending how into rep you plan on going).
Then there is the whole getting magic items thing. Unless you can combine reps via factions (rep with certain factions can get you specific enchantemnt types or specially crafted items that you can combine into one item) getting magic items could be a problem.