OP, do you actually care about your credit score? It's only relevant if you're actually planning on getting a loan in the near future. If not, then apply away, since you'd only need your credit score for more cards. And it's a self correcting problem - if you have indeed applied for too many credit cards to hurt your credit score, then you won't get approved for new cards. I tell this to anybody who thinks I'm trashing my credit score by applying to a bunch of credit cards (because some people refuse to believe that cancelling a credit card won't necessarily drop your score).
Your credit score is made up of 5 things, in decreasing weight
http://www.myfico.com/crediteducation/whatsinyourscore.aspx1) Payment history
2) Credit Utilization
3) Length of history (your oldest card, newest card, and average)
4) Types of credit accounts (fixed monthly installments such as loans, variable charges such as credit cards)
5) Number of inquiries
Numbers 4 and 5 are actually tied in weight.
When you apply for a new card, you get an inquiry, which will drop your score by a small amount. It will also decrease your average age of account. However, if you have a card or two that has a long history already, this effect is minimal. On the up side, if you keep your spending constant, your credit utilization will go down, as you now have more credit. Credit inquiries stop affecting your score after one year, although they stay on your report for two years.
When you cancel a credit card you've churned, your credit score will probably go up as long as you drop your spending a bit. Why? Well your average age of account just went up (assuming that this card is younger than your average age of account, which it should be if you're churning it). But your credit limit went down, so your utilization will go up unless you drop your spending proportionally.EDIT: When you cancel a credit card, a closed account ages with the rest of your accounts, but drops off your report in 10 years. So as long as you lower your spending proportional to the loss in credit limit, cancelling a card won't affect your score.
http://ficoforums.myfico.com/t5/Credit-Cards/Closing-Credit-Cards/td-p/347190Oh yea and Amex will backdate your cards if they can find records of the first time you opened an Amex. Any new Amex will be backdated as having been opened in the year in which you got your first Amex, and the month in which you actually applied to the new Amex. So it's possible to actually increase your average age of account by applying for an Amex.
http://ficoforums.myfico.com/t5/Credit-Cards/Amex-and-Backdating/m-p/1124167#M313576Another data point - I only started with my first credit card September of last year, and I just went on an app spree for four cards and now have eight. Credit score is 711 according to Credit Karma post app spree (but Credit Karma is only an estimate, which tends to underestimate in my experience). Score before app spree was 724 (actual TransUnion credit score from Barclays).