I have two lens currently for my camera. An AF-S DX VR NIKKOR 18-55mm f/3.5-5.6G (kit lens) and a AF-S DX VR Zoom-NIKKOR 55-200mm f/4-5.6G IF-ED lens. I have found that there are cases when the 18-55mm is too short and the 55-200 is too long. I have looked at a 18-200mm f/3.5-5.6G AF-S ED VR II Nikkor Telephoto Zoom Lens but I cannot currently afford to pay 1300 (USD) right now. I have also looked at cheaper options like a Tamron AF 18-200mm f/3.5-6.3 for $300 but then I get concerned about the quality. (Note: I am not printing my photos)

So my questions are this: First are lenses like the Tamron really worth anything? And if I was to purchase a lens with the range of 18-200mm why/when would I use the other lenses? Or does it come down to I should learn to switch my lens faster?