Yes, practise in Shred really improves playing in other styles as well, probaply because most technical "restrictions" are removed. I've been pretty into Jazz last year, and I wouldn't have been able to do it if I hadn't already reached speed levels beyond the ones required for Jazz, so to speak. And I guess the effect goes the other way as well: Jazz makes you think more about what you play. Not just licks and scale runs, but musical phrases. Lately I've tried to do "intelligent" licks fast and improvised, and it's tough, but it's cool to see how gaining skill in one area improves your skills in other area's as well, and shredding is one of the most important ones, I guess, because it removes those "technical restrictions".
Forgive me if I sound too much like someone being filosophical about his hobby or job