Canadian High Interest Savings Bank Accounts

Ok, experts in rewards and credit hits, I have a question which requires your knowledges and opinions.

Here's my dilemma: I never use amazon.com to shop but I have to replace some parts on my road bike and the only place where it is in stock is via amzon.com. Now those 2 parts come to a total of $43.40 and when I come to checkout I got this eye appealing interesting and captivating offer that says I can save an instant $30 if I do sign up with the amazon.com Visa card and make my purchase with it!

The fine prints are all available on the amazon website: http://www.amazon.com/gp/cobrandcard/marketing.html/ref=cobrand_ch_t2_huc_mr/188-1082663-2329025?ad=T5A1&plattr=math&imp=32088779961&pr=con321&inc=30stmt&place=huc

Get the Amazon.com Rewards Visa® Card and you'll automatically get $30 back after your first purchase.

Get $30 Back
Your Amazon.com Visa Card account will automatically be credited $30 within a few days of your first purchase with the card. The discount will appear as a credit on your credit card statement.
Get Instant Credit¹
Instant use of the card after approval.
No Annual Fee

So the dilemma comes to, is it worth a credit hit on my record to save $30 on an order of $43.40? I don't need the bike parts right now, it's just pure esthetics since these parts still work fine but were damged when I got my bike crash during my race 2 weeks ago.

I already have the MBNA SmartCash, the ScotiaBank Visa L'EARN and the NB Ultramar Mastercard so I'd use the amazon.com just for the $30 and then forget about it like I did with my Ultramar after I got my SmartCash.

I currently have used most of my credit available on my MBNA Smartcash and I have scheduled my full payment online 2 days before the deadline of my statement as I always do to earn the most interest possible from my HSBC account before paying my bills. Should I clear my total before asking for this card thus enhancing my chances of being accepted since I don't know my credit score?