Traditionally Hen Hud LDers have done well going to Iowa, which is directly after school ends, and even occasionally before school ends, meaning that a Regents exam may need to be taken in August. Worse things have happened, but it's still a pain in the butt. Other Institutes worth looking at are Victory Briefs, NSD (National Symposium for Debate), and the Ivy Scholars program at Yale. NDF (National Debate Forum) is also highly recommended.
Are institutes worth it? Well, overall, I'd say yes. You learn a lot of stuff you don't get at weekly meetings, and you focus your commitment to the activity. I say go for it if you can.