First off, I recommend that you determine your current Credit Card balance, and how long you expect it will take to pay it off. Figure out how much of your payment will be going towards the CC's interest, and how much interest you will be paying in total. You need this info to make an informed decision.
Now you can look at the Credit Card offers and compare rates. Figure out how much you will save by lowering your interest rate. Remember that with a lower rate you can pay it off faster while making the same monthly payment. However, there are some things to watch out for in the fine print of the offer:
Balance transfer fees for the new
card. You'll usually get charged a
fee of $50-100, or a percentage of
the balance. Make sure this fee
doesn't exceed the interest rate savings on your
Is the rate for balance transfers
temporary? Will the interest rate on
your balance go up after a few
months? If so, will you have it paid
off by then? Or will you be right
back where you started?
If transferring the balance is going to save you a reasonable amount of money (enough to make the hassle worth it), then you should probably do it, assuming you are financially literate enough to understand how it all works. (Don't make a financial move you don't understand.)
As for your concerns:
Having too many cards and losing track. There is a legitimate concern there, but look at it this way: If your old card isn't competitive (which it probably isn't if you're transferring the balance elsewhere), then it's probably time to close it. You don't have to keep both cards around. And if the old one is paid off, it can sit with zero balance for a while (no payments to be made).
Note that a new card is not a license to spend more! You are getting the new card to reduce your total debt as efficiently as possible (by paying less interest). If you are worried that you will start buying things with both cards, then maybe this isn't a good idea.
Having "too much credit" available. This is not a problem for most people. Is your FICO above 800? If not, don't worry about it. What you should worry about is:
Credit Utilization - What is the the total limit of all your credit cards? What is the total balance of all your credit cards? Divide these numbers to get your utilization percentage. If this gets too high (you are maxed out), it will hurt your score.
Debt to Income Ratio - How much do you owe (Credit Card, Car Loans, Mortgage) versus how much you make? If this number gets too high, it looks like you are in over your head.
So, what will happen if you apply for a new card and transfer your balance? Will your total debt change? No. So your DTI ratio will stay the same. Will your Credit Utilization change? That depends on the credit limits of the old card vs new one, and whether or not you keep the old one open.