I heard about all these bonus mileges when you sign up for a credit card. I didnt really cared about those stuffs. It was partly becuase I didnt know how those stuffs works. But now after in depth research and careful consideration, I think it can be very rewarding to have those cards. Any body here uses any mileage cards ? airline loyalty cards?

Well what I meant was, you airfare is coming cheap mostly for two reasons: off season travel and larger airport departure. So, the milegae redeem could be a good deal if you were travelling on a peak season and leaving from a smaller airport.

Since you dont have an airline credit card, why dont you apply for one where u can transfer your bank card miles. That way you will earn at least 30k bonus miles in addition to your 56k. That should earn u a free round trip ticket to ktm from any airports in US

 My current card is a card that allows me to convert my points for airmiles that can be redeemed for various commodities. Applying a specific frequent flier card would be as insignificant as someone applying for an airline card despite already having one. It'll lower the credit and most of them come with an annual fee. (Canceling credit cards prior to completion of one year period to 'save' annual fee will lower your credit score). 

Do you know why credit score decreases when you cancel your credit card? Yes it does decrease but not for long time. If you are one of those ppl who doesnot carry a balance, you will be fine. When u have an extra credit card, your credit utilization percent decreases so after canceling the card, credit utilization increases little bit. So, credit score goes down for some months. This is just temporary and you will never have a some sort of derogatory effect. If you are applying for a mortgage loan or any sort of loan with in couple of months I wouldnot advise it. If not, apply for a credit card with an airline enjoy the benefit of priority boarding, use of lounges on your way to KTM and cancel when u get bk.

BTW, most of those airlines card doesnot have any foreign transaction fee which could be a plus.

can we use mileage for duty free shopping?

You can use those cards for any kind of shopping but u have to see the terms and conditions to find out if you can pay with mileage.