Shadow seems to be a perennial sleeper, so I would agree that it is undervalued compared to other pins.
I bought mine for $1,100 probably 10-12 years ago on the endorsements of so many on RGP never having played or seen it in person. For the time it was made, the Sanctum lock was an unusual use of a playfield magnet, to propel the ball up into the lock. I like the mini playfield feature. The diverters are a bit clunky, but they give the player a lot of options as to how to set up the next shot, so for me they add to the flow of the game. You have an inner and an outer loop and two saucer shots, one off the inner loop. I think it recognizes up to either a five or seven way combo, suggesting the designers had flow in mind. It has one of the best video modes I have seen. It has six modes that mix up the shots well, and has four multiballs including the wizard mode, but I don't think that there is any stackability. Getting to the wizard mode is pretty straightforward and of moderate difficulty, and the wizard mode is very hard to accomplish, you need to shoot well and strategize your shoots to accomplish it. I think the sound and especially the animations are excellent. It has no pop bumpers, which isn't noticeable during play, another feature I think is unique. Seeing the movie helps get the game. which I really didn't until I saw the movie.
It has a horrific backglass, and it is too dark to play in the dark at least for me, which is why I made a lighting kit for mine. The flippers have a different feel than other B/W games, which to this day I cannot figure out why.
It is a keeper for me, for it offers a lot. Mine is in excellent condition (9++ on both pf and cab), and if I were to sell it, I would price it around $3,500-$4,000, so IMO you are on track with pricing it. Mine is not a players pin, not restored, but for sure CQ (whatever that means anymore).