I'm using 6.04d with some hacks, if I upgrade do I have to reinstall the hacks and what's the benefit of upgrading?

You'll need to re-install them... a few benefits are cleaner code, improved search, and the latest modifications

I'd wait until 6.1.0 is outta beta before upgrading tho... another week or 2, they are redoing some of the guts to make it more stable.