Yup, there's not doubt that speaker cabling can make a pretty big difference. That's why I always try to keep the speaker cables as short as possible...even at the expense of longer interconnects.

If you have relatively "tame" speakers in terms of reactance, it's not that big a deal. If you've got "difficult" speakers with one or more big fat woofers, you can (and it's easily audible) overwhelm an amp with insufficient damping. This was more of a problem back in the tube days, but it can still bite you in the hiney with the wrong amp/speaker/cabling combination.

Cheers,