The only way I can see that it would be "bad" to save too much is in situations where the money saved is taken away from immediate survival needs. For example, if you choose to save money rather than pay for heating or food, then you're probably saving too much.
Other than that, I don't think it's possible. The article's premise is that there is an optimal balance to saving and spending, and if you're too far on the savings side of that scale, then you're depriving yourself and saving too much. The problem with that argument is that optimal balance is subjective: one's person's needs is another person's luxury.
To answer the OP's questions directly:
Is there anyone out there who regrets saving too much? Specifically those of you who are over 40?
No. I just turned 40 two days ago, and I've never regretted saving too much. In fact, the opposite is true, I regret not saving more and not finding FI/ERE sooner. I've spent a lot of money on "stuff" in the past, and almost none of it has brought me any happiness or fulfillment. It might sound cliche, but my favorite things in life are eating, drinking and playing cards with friends, or "making things", whether it be software, scale models, home improvements, etc. Because I haven't saved enough, I still have to work a job I don't absolutely love, which takes time away from these things. Today, the more I save, the happier I am, because it brings me that much closer to freeing up my time for things I want to do.