^GSmith, using a smaller aperture (f/higher number) may help, at 2.8 (which you used) the lens may well be wide open or not far off (lets more light in but shallow depth of focus and generally soft performance). as for what aperture, well theres no set rule I'd go for f/8 as my lens works better here, some would go for f/11 or f/16. note for every stop (google the values as its not linear) you will have to expose for twice as long, but the results are worth it. Make sure your lens is clean. I cant be bothered googling but i think your camera is one of these new fandangled micro 4/5ths [edit just reread and its not, but the sensor is smaller so same still applies], in which case the sensor is a bit smaller so your equivalent aperture value (in terms of depth of field and lens performance) will be a bit lower, Im not sure how much etc, but if I had your camera (no insult from what i have seen they are good, and I think they will be very good for exploring, to many people feel they have to carry a big SLR everywhere) then I would probably go for f/5.6 (which is 2 stops above what you had so would require a 30 second exposure) the end result would be exposed the same but be sharper and may or may not solve the lens flair (and if the aperture goes very small you will get a more intentional flare of stars on the lights).
make sure you confirm the camera focuses on what you want, and use a remote or simply the 2 second timer to prevent shaking the tripod causing blur.