I am not Cathe but I am in a similar situation as you are. I would say that taking breaks is not hurting your progress or lessening the benefits of the workout. I say this because I used to have to take a lot of breaks during certain workouts (particularly MIC and the IMAX's) but now I can pretty much do them straight through. I figure that if these breaks were taking away from the benefits of the workout, I wouldn't have progressed so quickly. I think working towards taking fewer and fewer breaks is a good fitness goal.
Some other thoughts: remember that your body is smart... it tells you when it needs to stop (for whatever reason). I learned the hard way that it is best to listen! Lastly, I would make sure that your breaks are not too long. Going quickly from when end of your heart rate zone to the other is not good for you... I would try to limit the breaks to no longer than 30 sec. to one min. This approach worked very well for me. I hope this helps you! Good luck with your goals!
Alison