I use a SRM since several years and love it to a grade that I think biking is not possible without one.
I am a poor swimmer and have to roll up the field on the bike. So I use my powermeter to really ride smart and get the most out of my power. For me, pacing however is a complex thing of effort, heartrate and watts. In a race most reliable is HR - but not in the first hour of racing, where my HR always is elevated. So in the first hour I ride on target watts. Then I try to hold a target HR - whatever watts this might be. The least reliable thing in a race is effort, which moves up and down even if HR or Watt are steady, depending on lots of things like, nutritional status, crowd, mental status, expectations etc.
Basically, the powermeter is most helpful to keep my effort rather steady - keep the power down at the beginning of hills and avoiding these short bursts above your LT which can kill you; and on the other side keeping my power up on the flats, which is tough, since maintaining the same power feels much harder in the flats than at the hills.
While I think it is not possible to plan your training by your power numbers, the powermeter gives me immediate feedback of what I am doing. For me, HR is differing depending on the training/nutrition of the previous day by 15 beats for the same wattage. Perceived effort for the same wattage is differing even more depending on nutrition, duration of workout, accumulated training stress etc. If you do a 4h steady ride, 250W might feel ridiculous easy at the beginning, but really tough at the end of the workout. It might feel that you are pushing 100 Watts more, in fact you are struggling to keep the same effort.
With the objective numbers of the powermeter, you have something to relate your perceived effort or HR and you are getting a better picture of what you are doing and what your condition/tiredness is.
Another thing I like about a powermeter is that you can read your competition quite easily. Riding with them for 2 hours gives me a good picture where their threshold is and what it would cost me to drop them. If I decide to do so, I go not like crazy, but just 10-20W about THEIR threshold and I drop them within 10 minutes.
Since I joined TeamTBB I train a lot more and the powermeter plays a minor role. It is most helpful when your training time is limited and you want to get out the most of your invested time. For example I used to program it so that I could see the time I did not pedal. This helped me to reduce this time on a flat 4h ride from 35min to 4 min.
If your ride in a group, you have to go with the group - whatever your powermeter says. If you ride a lot on your own, it might be a great tool. Same in a race, the more you are in the top rang and ride in front of the pack, the more you have to ride by tactics and competition rather than by a powermeter.
For some, using a powermeter is like painting by numbers. And riding without any tool the real art of sport. But I think it is not the worst thing to use it to become a Picasso.