Amex's currency exchange rates are quite reasonable -- much better than cash or traveller's cheques, and no purchase commission either. As a Canadian Platinum Amex cardholder (points acceclerator is included) I feel very smug every time I look at US purchases on my card.
While you might be paying a small amount on currency, your are getting an extra 1.25 points, or about 2.5 cents worth of points, on each US dollar spent. I think that would make up most of any currency loss. This presumes of course that you are willing to pay extra, just to get the extra points.
Checking my statement, it appears that for US charges, I am paying a premium of about .4%, or about 80c on 200$. So by paying an extra 80c, I receive about 265 points extra. That works out to about .3c US per point, or about 1/7 the cost of buying points.
I suppose you would have to figure out the additional cost to pay in CDN dollars as well, but it still looks like a good way to earn extra points.
Regards,
Ken Hamer
[This message has been edited by KenHamer (edited 04-26-99).]