You'd think so, but there's a lot more to it.
Look at the rules for nearly any promotion and there will be a clause in there that says
Use of any automated program to enter will result in disqualification.So first and foremost, you're breaking the rules.
But what if you're not concerned about that? What if you'll take the prize and not feel guilty about it?
Well, it's not that simple. Nearly every promotional agency worth its salt has many layers of very sophisticated ways to detect and automatically disqualify entries from automated entry methods.
So in the end you're paying a service to submit "hundreds or thousands" of registrations (Do you really know how many they really are submitting and to what promotions?) most of which will never even count.
The registration service gets their money -- they win. You don't.
There are only two ways to consistently win prizes from these games. One is by becoming an expert, reading blogs and posting on message boards and spending a lot of time each day on your hobby. The other is by using Win.ly, which will allow you to spend just a few minutes a day and quickly enter just the games worth entering.
Of course the experts could also benefit from Win.ly. :-)