I missed last year but I usually go every year because I live locally. Each year there are different plant vendors there so you never know what you will find. The heirloom society of Landis Valley has pretty much the same plants each year. But a lot of those plants can ONLY be found at Landis Valley. I have friends who drive up from Maryland each year and make a day of plant shopping at all our local greenhoues too. If you do go, bring a large basket or wagon because it is a lot of walking though out the grounds. They also have "plant sitters" so you can park your purchases and keep on shopping!
Enjoy.