I wouldn't park my NSX in Baltimore at all. We have a parking pass for the Pratt street garage and those spaces are TINY. My wife's CRV is dented up from years of parking in there. I'm about 45 minutes north of Baltimore, you can leave your car at my house and take a cab in if you want.
All the underground parking that i've been in have very small spaces. Call ahead and find out if the valet services will be responsible if any damage occurs. I would also do a walk around the car with a supervisor before hand and take pictures for proof in the event that your car gets dinged.