We've flown from EWR to MCO three times and from Atlantic City once. I've had no problems with Spirit and my husband actually perfers it. The flight is shorter (I know - by about 20 minutes) and the less time he spends on a plane, the better off we all are. Also, he has some issues with going out of Newark since 9/11. He'll do it, but not without concerns.
I think EWR is very effiecient and Atlantic City is very, well, simple. However, they are very thorough - to the point where I had to take my shoes off for the random security check.
Last time I checked, the parking was $4 per 24 hours. We've never left our car at the airport before, but our chauffer (aka my mom) balked at the idea of getting us to our 7 AM flight.
The flight times (out early, back late) and the lowest fare we've paid yet are what convinced us to go with Spirit again for our February trip.
Don't expect much from the airport itself. No big gift shops or restaurants like at MCO and EWR. But it can't be beat for convenience.
Keep in mind that Spirit will give vouchers if the fare goes down, so don't hesitate to book.
Have a great trip.