One other quick note: Most reports on Juniper suggest they will decline an app for a product for which you already have an open account. When I did the Juniper churn, I closed my existing account before applying. After approval I was then able to reopen the older account. YMMV.

What is the best strategy to take if you are denied for having sufficient available credit with a bank? Close cards? reduce limits? or both?

Why would you want to reopen the older account, esp you only go after the sign-up bonuses?

On the other note about "reference number" - I am not sure every card application gets one. My current experiences are there is none for UA and none for AA either. Dont remember how it was few months back.

Both...close cards if it is a new one...keep the oldest open the longest

To combine the credit limits and/or keep the age provided by the older account. If neither of these is a factor, the older account can be left closed.
I've only seen it on a decline letter or a request for more information/verification letter. It seems unnecessary for approvals since there is no further follow-up.

As soon as the card arrives to your residence you should be calling the issuer and asking them to reduce the credit limit to the minimum they allow for that particular card (usually around 5k but it varies).

Depending on your specific situation card issuers can decline you for too much credit, even though it was issued by another bank.

I once got such a letter from Citi and they offered to divide the credit line on an existing account. I didn't really like the allocation they proposed, so I called and had a different amount allocated from a different card and they processed the approval for the new card.

I would imagine other banks might also offer you a similar option in such a situation ("we cannot extend you any more credit at this time, but we can issue a new card with a portion of your existing $x credit line"). Even if the letter does not explicitly say so, you could call and discuss this with a credit analyst.

Reducing credit limits leads to higher utilization, which is a negative score factor, so the strategy of voluntarily reducing credit lines is one to be undertaken with care depending on your FICO score, how much other credit you have available, and your overall credit situation. (Generally the "too much available credit" reason only comes into play for people with a VERY large amount of unused credit, who would tend to have high FICO scores anyway.)

Or if you're churning 8-12 cards a month.

In our case Citi seems always just make a phone call and offer to move some credit line from one that is very underutilized (usually it is used between 5% to 10% and a quite high credit line to begin with because of its age.) I never receive a letter from them, but a couple phone calls in the past. I dont know how much one's FICO would be affected - that a particular card with long history has the line fluctuated every few months as the credit line together w/statement balance is reported each month.

It is a very much YMMV thing. Sometimes banks do crazy thing - Chase once called me on a cancelled card that had a very decent line. The woman offered to add that line back to one of my open Chase cards. I took it just to get her off the phone and the line sure was added back to the card I named. I then called Chase to get rid of the excess. Nutty.

I tend to think that FICO is only the initial factor banks use for approval. There are lots more variables come into play beyond FICO.

In practice, this would have the same effect, wouldn't it? (a large amount of underutilized credit)