as I am in a similar boat, I have done a little research on this topic.
From what I have seen, reapplicants have a slight edge over 1st-timers in terms of selectivity. Reapplicants have about 5% higher acceptance rates (15% for 1st time vs. 20% for reapplicant, for example.). We also have an advantage in that the adcom has already seen our application, and if we can get feedback from them, we will know specifically what improvements they want to see.
We have a much easier time showing our committment to the program by reapplying, and this further illustrates our dedication to our goal.
The adcom will have specific expectations for us though, and this puts us under more scrutiny. We have to be careful looking at our previous year's app, to see what we talked about, and make sure we meet those expectations, show a lot of growth, and show that we took every opportunity to grow. If you talked about running a marathon this coming year, did you? Did you get that big promotion you were in line for? Did you take all those classes you assured the adcom you would take in your optional essay? etc, etc.
As this coming fall should be even more competitive than the past several years, we have to be sure to put our absolutely best foot forward. Also, APPLY EARLY. I guarantee they will say that in your feedback if you didnt apply the first day.
Have fun this year, do all that you can, as thats all that you can do. =P