just be smart about it.

1. don't spend more than your available credit every month at office supply stores
2. use your ink card for other purchases
3. don't max out the 50k year max at office supply stores

I would say $2,000 to $2,500 is a good spot. It generates 10,000+ points per month and you avoid the 3 rules above. Plus at that point you are already spend over $70 on gift card fees.