Now I am only starting week 4 using PCs but to address the comments since I have in the past done all 4.
- Single Leg drills on your trainer: Most all of us have a trainer. Single legged drill are a pain in the butt. I for one would do them, but would get crazy bored after an hour. Using PCs I definately can tell I am getting a better workout from just doing one legged drills off my trainer.

- Riding in the hills/mountains to improve peddal efficiency: Any issues with your pedal stroke will be apparent when pushing uphill. Some of us offseason folks do not have this option of riding hills during the winter months which are key to base development. I have had my share of parking garages during Dec. Will still it, but not as often.

- Cycle or spin class riding out of the saddle only: Try it for an hour long ride or class you will see I was able to stand up for the first time on my PCs yesterday, talk about creating efficiency. If you can do this your pretty damn efficient. Now I am not saying I am an incredibly efficient cyclist. I was up on my cranks for about 2 minutes during a small little climb, but eventually I will work my way up. Also in my opinion Spin bikes teach bad skills. 1) It's not your bike and you are not going to be able to replicate the positioning 2) Crank length usually isn't adjustable. I think they just lend to bad form. (IMHO). I have used them in the past to build legs strength on the down stroke, will continue to do so, but I don't think you can compare the two workout to the benefits of PCs. It would be like comparing it to squats.
- Volume, volume and more volume I agree with you here, but time is money and time away from Family. I haven't given up my long ride just yet, but all my other rides right now are on PCs.