To provide another response to your original questions:
"1) do lenses lose any image quality because of the magnification factor on non-full frame sensor cameras?"
No - not just because of the size of the sensor (which is what causes the so-called "magnification factor" or "crop factor"). However, the same lens may provide a better quality image on an FX sensor than a DX sensor simply because of the specific sensor used in each camera and based on how something as nebulous as "image quality" is determined. Most FX sensors have better dynamic range and better noise performance than most DX sensors, so that alone could make an image "better quality" if these happen to be critical factors for a particular image. But if an image is captured under conditions where these particular FX sensor advantages will have little or no effect, then there will likely be very little difference (if any) in overall image quality.
"2) does Ai conversion cause the value of old lenses to drop?"
In general, no. This would occur only if the lens happens to be in high demand by collectors. If it is, then any change from its original form will decrease its collectable value. For lenses that are not considered "collector's items" the AI conversion may well help its resale value a bit.
"3) if my old lens has some small specs of dust that dont appear on film, will the dust particles be more likely to appear on digital?"
No. It takes a LOT of dust, or some very large particles, to have a visible impact on an image (with film or a digital sensor). With lots of dust there may be an overall image quality degradation along with a loss of contrast. But a few dust specs in a lens, especially if toward the front of the lens, will have no visible impact on images. Dust on or near the rear element of the lens can have more effect on images, but even there it takes quite a lot of dust to have a visible impact.