I agree that using power is a great way to set up a training regimen, and that it does seem to be state-of-the-art, as power is the gold standard for pro cyclists.
I don't think one needs be a racer to take advantage of either a training regimen or using power to base one off, though the cost of investing in a power meter needs to be weighed in any considerations.
To your question of what else to measure, you are certainly still monitoring your HR, no? And of course cadence monitoring. Those three are really effective parameters for dialing in your training, and ultimately, your performance.
Outside of biometric measures, having GPS info allows you to see what geographic features impact your performance, most critically your climbing performance, which you can track with VAM (vertical ascent meters) if you've got real hills. With the new Shimano Di2 gear position transmitter, you can also overlay gear selection to these other parameters and really drill down to a new level of training detail and specificity.