I'd submitted a support request online last evening but had got no response by this morning. But I managed to solve my particular problem.
For anybody else getting my "error code [1001]" error when trying to add their prepaid credit card to their kobo account, it seems that the kobo store is trying to validate your card by address. For the Vanilla Mastercard in particular, you can set the Postal Code online at
www.vanillamastercard.com to pretty much anything you want.
I suppose that technically I could have changed mine to something in, say, Alberta. That would have saved me $1.20 per month as they don't charge PST there? It's a difference between $15.75 ($15+GST) and $16.95 ($15+GST+PST), and $0.85 more than the total on my card over three months, dangit. I wonder if Kobo will take any funds off the $10 credit they gave me when I registered my Touch? Otherwise I'll probably be getting a $35 Visa every other month instead of a $50 Mastercard every three months.