I shoot a lot of wildlife stuff and I love my 70-300mm. Actually I want a bit more reach and have been checking out the various options and their prices so for this reason I would have found the 50-200mm a bit too short.
I think you can work around your gap in focal lengths with your kit lens and a 70-300 by just moving forwards or backwards but that extra 100mm of reach the 300 has over the 200 is not something you can usually get past.
That said I borrowed a 55-200 for a month and while I had it I never changed lenses as it covers most situations (except wildlife) really well and is easy to carry around being significantly smaller than the 300.
As people have said it all depends what you want to do with your camera.