My experience is probably not typical working in the utility industry, but I can tell you that it really would not work out at my office.
Here's the issue at my work: managers come to have low expectations from chronic underperformers. They accept poor performance from them, giving them average raises, etc. These same poor performers would probably take a lot of these "unlimited" paid days off, and since expectations of them are already low they will not be penalized. In my line of work, you only get fired if you are doing something against the law or you just don't come in to work at all, so becoming expendable is not a concern for poor performers.
High performers get above average raises and better promotion opportunities, but above average raises vs. average raises is probably a difference of 1-2% or so. High performers may have a better shot at getting a promotion, but promotion opportunities are limited so the top 10% performers may get those opportunities but the rest of the high performers are stuck high and dry. Promotions do come with increased pay and benefits, but also proportionate increased responsibilities.
The net result is that poor performers will essentially become validated in their poor performance. The expectations for them are low, so they will no longer be doing anything wrong by just leaving work. All they have to do is say their are getting their work done. No change there from what they have been doing before, except that it is now above board. High performers will continue to work hard, but as studies have shown they will now likely take less time off than before. Their base pay differential will be about the same as under the old system, but the gap will close because of the extra time off that poor performers will get.
My GUESS is there isn't enough competition in the utility industry to make the workplace overly competitive and thus the rewards are somewhat neutralized? In other words, it is not like there is 6 or so utility companies in town fighting for the same workforce.