Been a long time owner of a 2011 elantra and just bought a 2015 elantra for the wife. Glad to join for some trustworthy correspondence and ideas for a few upgrades and problems I have had. Look forward to exploring the forum in depth!
In terms of upgrades, check out sharkracing.com for appearance and mild performance upgrades. There doesn't seem to be a lot of serious performance upgrades for the Elantra. The Elantra's corporate cousin, the Kia Forte, seems to have a much more robust performance community.