The stem cells themselves are most likely just as potent when obtained by either method, though Intellicell's process does yield higher percentage of viable cells as well as more cells in general.
The problem with enzymes is, like you said, contamination. In fact, it is an active contamination, because enzymes will potentially keep working and catalyzing reactions as long as they exist - and you don't want to have any random reactions happening in that knee you just injected your stem cells into. Finally, when any biological cell is manipulated, there are SO MANY things that can go wrong. This is why clinical trials for any drug go on for decades, and then still, years after approval, it turns out something somewhere is causing cancer after all. Any large quantity of enzymes can turn cells into potentially harmful or cancerous - to alleviate that fear by clinical studies would require an enormous amount of money and time (think R&D budgets of large pharma). The body is an enormous and complicated machine, and you just don't want to modify anything at all if you don't have to. Intellicell does just that - it's just like taking out your own blood, shaking it up a bit, and then merely pouring it back into you. No harm is possible.