I just bought an 89 LT 250R in great, stock condition and you should definitely feel it when the powervalve kicks in.  It is not a "hitless" engine.  On mine it almost feels like a turbo.   The engine is pulling hard and then suddenly it is pulling really hard and the rear wheels are breaking loose.  Fun stuff.  I've read posts on this website that diss Suzuki's powervalve but I have to think theirs is either broken, out of adjustment, or maybe they've made mods to the engine that make it less noticeable.