I personally think it is. This seems like a dress I'd wear to go out with my friends on a weekend afternoon (not much of a night look either). It's very cute though so, unless you're the type to only wear dresses on special occasions, I'd get it for casual purposes.
Sticking to Urban Outfitters, I think that these dresses would be more appropriate for the event if you don't want to look super fancy but not too casual:
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=40321473&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=40390965&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=39452917&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=39037379&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=38825808&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=39774674&category=W-DRESSES-PARTY
http://www.urbanoutfitters.com/urban/catalog/productdetail.jsp?id=39401377&category=W-DRESSES-PARTY
Most of these are considerably more expensive than the one that you wanted so if you're looking for a lower price, I'd suggest you go to thrift stores or, if you're shopping online, try going to a more low end retail website. You could probably find something of a similar style.
