With respect to resale value, if the AI conversion is either done with factory parts, or done properly, the value typically goes up, at least here in the states. Collectibility value not so much. But, if I remember correctly, APUG is more about using the gear than letting it sit on the shelf collecting dust.
It looks like the lens the OP has is the last 50/2 pre-AI lens, just before the AI lens came out. So, rubber focusing ring, black barrel, and multicoated glass. In which case, I still think it'd be a good idea to find a parts 50/2 AI with the five screw mount and swap both the aperture ring, plus the rear element baffle piece to his lens. Once that's done, the lens will be AI, except for two things. The color and softness of the focusing ring grip and the serial number.
Both lenses would be digital friendly. For that matter, the E lens will produce pretty much the same results as the AF version, maybe with a little more flare and less contrast, since it's single coated. Otherwise, same formula.