Bear in mind that the Tamron is not the sharpest lens on the block, but is sharp enough and provides more fun per $ or ounce than most telephotos. One of its greatest advantages is its light weight and zoom. You nullify these by adding massive expensive gear that might get the best of a supersharp heavyweight that outresolves the sensor but might not increase the sharpness of a less refined lens.
I think we will have to agree to disagree on this point.
Whilst I don't think a 5 series Gitzo is necessary a good Feisol 2/3 series (or similar) with a decent Gimbal would net the best results without spending silly money.
Whatever the price or weight of the lens, it is the focal length that matters. You state that the Tamron is not the very sharpest lens going, surely this makes getting the very best out of it even more important?
If light levels are good then no support is necessary, but that isn't always the case.
Getting the best out of a lens means appreciating what its weak point is. There are mathematical equations to describe the overall resolution of a system in terms of reciprocals of the resolution of the lens, the resolution of the sensor etc. If the resolution of the sensor is low, then it dominates the equation, if that of the lens is low, then it dominates the equation. Under such conditions, the other factors are less important.
In simple terms, if you have a very sharp lens, then every small blurring event, such as minute camera shake, will be noticeable. If you have a very soft lens, then a minute amount of camera shake would not be noticeable in the overall blur. So, you would be crazy to hand hold a 600mm f/2.8 II with IS off, or more sensibly a 400 mm f/5.6 at a low shutter speed. However, a Tamron 150-600mm at 1/1000s with IS on would not register any camera shake.
As Weixing write there is no wrong or right way, but you can have accessories that are overkill for a particular lens.