As a rule of thumb, the top model of anything (CPU, graphics card, car) is always lots of extra money for little extra value. A Quadro costs several times more than a comparable GeForce, but the difference in performance will be just a few percentage points - in my opinion, not worth the extra expense.

The best price/performance ratio is usually around the middle/upper middle, on the NVIDIA side of things I'd say that currently the GTX 460 gives you a lot for the money.