As mavendrill said, the costs of college are highly variable and, unlike FI planning, they are concentrated in a few areas, none of which you control. So whether or not you are saving too much depends on which scenario you are most comfortable with:
1) Not saving anything; the kid will have to borrow / work for anything they want to do
2) Saving enough to be a big help / pay for most of it. The kid will need to borrow / work / get scholarships for the difference
3) Paying full freight for college. You might save too much, which will leave you wondering what to do with it. But your kid will start their working life debt-free.
All I can offer is my strategy, which is somewhat of a blend of #2 and #3. I am saving $10k per year (my state's maximum tax deduction) for my son for years 0-4. That $50k will have 14 years to grow, so I expect when he enters school I will have $100-150k. I expect this will make a good dent in any education he wants. For the difference, I expect funding will come from one of several sources: his work / savings, my work / savings, his scholarships, or his borrowing. What option we go with will depend on his state of mind and life goals. If he's a bit of a slacker, then I think it would be appropriate for him to have "skin in the game" on his costs, to keep him mindful of just how expensive it is, and not to waste the opportunity. If he turns out to be profoundly gifted with a desired interest in a field that will be both well-paying and likely beneficial to humankind (i.e. technology, medicine) then I will expect some scholarships and would deem it worthwhile to keep him focused on his studies rather than be distracted by some low-paying campus job. (although a research assistant position would be good) If he is just as gifted but wants to pursue a field that does not pay well, then we will have to see: I will want to support his self-actualization, but we will not want to set him up for a lifetime of financial difficulty.
I see the middle-of-the-road approach as giving me flexibility to answer any of these possibilities, without committing so much to 529 that I expect to have a big surplus at the end with a penalty withdrawal or having to get involved in my wider family's similar choices. I do expect FI within 5 years, so our situations are similar there, although I don't have ongoing funding planned. I have no problem picking up work for 4 years or so that would cover tuition. If it could be seasonal work, all the better.