Single database schema or multiple schemas?
the 'cleaner' solution would definitely using a single schema, and relate your data to a specific event, either with a EventID column, or yet better, using an Events table, relating your data to a row in this table (but keep it simple, you don't need to relate every row in every table to your event, just the 'top-most' objects)

but on the other hand, maybe 'You Aint Gonna Need It', a lot can change in a year, and you'll probably have to make a lot of changes and improvements for next years event. anyway you'll find yourself carrying over and migrating data which nobody needs or wants, so you may end up purging your database after all.

i learned to stick to the YAGNI rule the hard way several times, and keeping things simple always proofed to be the better solution. as long as you produce clean and maintainable code, it's often much simpler to add functionality, than to trim unneeded (and often untested) fat