We have been going yearly since about 2010. Bring lots of DEET and Thermacells. Secure your coolers in your vehicles. Do not leave food unattended. Do not get within 10 feet of the horses.
If the weather has been dry for the preceding two weeks before arrival, skeeters should not be too bad. Otherwise, be mindful that skeeters can be a problem in bayside breezes, overcast skies and nighttime; so, spray yourself with DEET and/or carry a Thermacell.
Make sure the screen door is closed promptly. Bring tiki torches and citronella candles. Smoke from campfires ward off the skeeters, too.
That said, by being prepared, we have enjoyed our visits.
We stayed once at the state park and the rest at the national park. I hear that the comfort stations have been renovated at the state park. At the NP, there are crabbing, clamming and paddling programs run by the rangers; so, take a look at the schedule.
En route to Chincoteague is a NASA visitors center at Wallops Island. Check the event schedule.
We are going during the first week in August.
Have fun!