There really needs to be a poll to decide how often they change the events it seems; Assuming the faster car categories attract more experienced drivers, I would expect they would probably want a weekly change, whilst the less experienced drivers would want a daily change......but really at that rate, they'll be trading the game in within a few weeks and complaining on GTP how boring it has become!
Edit: The only thing that slightly bothers me with Sport Mode is the emergence of too many categories which pretty much kills off one or two already good ones and dilutes the rest with many not really knowing where to race. People often end up going to other platforms etc as well. It also happens in real Motorsport and in RC cars which I used to do, where by far the best racing categories were simplified into one or two very large classes in certain areas of England and everyone from top to bottom had a ball. But this is sim racing where resources are almost limitless so we can afford to have really good concise competitive categories. As it stands, you wouldn't want any more and Super GT is due sometime soon adding to the confusion because it will be somewhere between Gr.1 and Gr.3.