I am not a coach and can only speak as a user but I have a few thoughts. I have been training with power for a little while now and have worked out whats best for me.
In my view, training works best when you have a goal, a target. What do you want to achieve? Is it weight loss, or getting faster by raising your FTP...
Target those intervals that will best help you reach your goal.
Doing intervals 4 times a week may fatigue you both physically and mentally. I know I struggle to find the motivation for intervals more than twice a week, what with work and family. Getting quality rest so your focussed is just as important as doing the training properly.
Have a look at the Flamme Rouge website;
http://www.flammerouge.je/content/3_fac ... sheets.htm
They have a good discussion on fitness vs rest. The key message is 'Recover your way to Success'.
So set your target, perhaps start out with two interval sessions a week and a longer easier ride just for fun. Train for a month, have a week of recovery, then re-test your fitness and set a new goal.
You will soon work out what works for you.