Welcome to the Newschoolers forums! You may read the forums as a guest, however you must be a registered member to post. Register to become a member today!
Above all else park boots are going to be MUCH more comfortable.
A big part of "park specific boot" is just a market, however in today's day and age there are very numerous features geared around park specific skiing that will make your feet thank you in the long run.
A few examples: more padding in the toe box to prevent toe bang (or SPK's rubber toe box), beefier power straps to prevent shin bang, cushioned tongue to help soften shin bang, footboards with a differing density of shock resistance materials, and the list goes on. In most middle of the road park boots, these features come standard.
If you're just starting off though, I think it's safe to say you'de be fine to sport your beefy nordicas for now just to get a feel. After a while though, your feet are probably going to start becoming fatigued if you hit park on a regular basis. At that point, you will definitly want to find new boots.