You do not necessarily need to use SONY lenses to get superior looking shots. TAmROn, Sigma and Tokina have made lenses for the Minolta-mount for years on end... and they work just fine on the SONY A100.
That certainly is some good glass. You will really unnecessarily overspend, using the OEM glass first. I, personally, would only spend my money on glass that I simply could not get any other way.