When I went to Florida in 2000, I did the exact opposite of what you're suggesting. I flew into Tampa/Clearwater and then drove to Disney for the day.
I've also stayed at the Holiday Inn Sunspree in Clearwater twice, once in 1996 and a few months after the trip above in 2000.
I can tell you that it is not a bad drive at all between Orlando/Kissimmee and Tampa/Clearwater. It's a little over an hour, and you should be fine in planning to head there in the a.m. sometime and have loads of fun, while still getting back in time for dinner and/or a show. One thing to keep in mind if it's a weekday is each urban area's respective rush hour, but most of the middle of your trek will be on open interstate highway. (be sure to check ahead of time for road construction too).
As for where to go or park, I can't tell you that, because I did all my water sports on the hotel's private beach. I haven't ever gone to any of the public areas.
I just wanted to reassure you, since no one's replied to your post yet, that the drive is not bad or long at all.
I love Clearwater!
Jon