I still believe that you "should" use quality lenses over the average or cheaper stuff, if possible, becuase of more than just the immediate image quality. Quality of build and precision of the glass elements helps to get that light just where it needs to be, and with less fear of distortion too,, be it barrelling, pincushioning, Chr Ab, cropping (DX vs FX lenses), vignetting etc etc which are all more likely to degrade your images and more likely to reside in the cheaper lenses. If this wasn't so, there would be no need for these more expensive lenses at all. Believe me, I am no pro and I'm not a rich guy, but I have learned the difference between budget lenses and more precisely built type lenses. What are they? Simple,, with the more expensive better quality lenses, you seldom have reason to moan over the results, whereas with the cheaper lenses it's likely for you to start doubting your gear and maybe even blame the camera itself... If you start off with good gear, then if a problem arises, it's quitle likely to be the photographer at fault, not always, but more times than not, rather than the lens...
That's not to say that all budget lenses will not perform. I can recall a couple of lenses I tried on my D300 a few years back and got some almost fantastic results. One in particular was the very cheap, 55-200mm, which was so dirt cheap I almost got suspicious of it at the time. Yet it gave some absolutely crisp, clear, beautiful results. Right now, I have the one leftover lens that I decided to keep when I cleaned out my small collection of lenses a while ago, the 70-300mm which will luckily fit on the D600 and 2 days ago I tried it out and was quite delighted at its results too. It's not a total cheap lens but neither is it expensive either, about half the price of my number one lens, the 24-120mm. I didn't even realize it was an FX lens and thought about selling it, but since it performed quite well on the D300, I decided to hang on to it - luckily.. I think I may have found a great duo for all-round use on the D600. While not trying to belittle anyone who uses budget lenses and thinks the world of them, I'd suggest you think of the quality which can be obtained from the better lenses as opposed to the quality you'd like to get out of the budget lenses.
I'm a builder by profession and I tend to buy better equipment when and where possible even if I have to wait a few weeks longer to be able to afford it over the hoards of cheaper stuff available. Not to show off, but so when you're on the job, the likelihood of failure is significantly reduced. Some of the brands of gear I buy, also have "home-user" ranges too, which I also stay clear of, because they are not made to do the same job as the full-on trade stuff. Building, photography, whatever,, it's all the same rules - better stuff will always cost more. Not necessarily bigger, just better...
Just my opinion... Hope I don't stand on any toes...!!!
