The Nikon S2 was my first experience in the Nikon RF system. I bought my first one in 2011 and since then have had close to 10 come through my hands.
In the last few years, every single S2 I have bought came to me with the slow speeds not firing right - either sticking open or firing at the same 1/30th speed regardless of setting. I've usually gotten these in lots with lenses and resold the camera and whatever else I didn't want. Anyway, I personally think the S2 cameras are coming up to an age where they all just seem to have issues in the slow speeds, due to failing lubricant or who knows what. BTW, some of these have come from dealers who advertised them as working properly...so there really isn't any guarantee here.
In terms of value, I have seen S2 prices creeping back up, especially for ones without issues which are apparently becoming more uncommon. With the 5cm f/1.4 lens, that's actually not a bad price IMO. I've sold cameras with slow speed issues for around that, without the lens. Let's not forget the 5cm f/1.4 lens has become a real cult classic.
Ultimately it's up to you...like already mentioned, the slow speeds aren't necessarily important depending on how you shoot. Factor in the repair if you need them and decide what it's worth to you...but I wouldn't bet on finding a similar camera/lens kit without issue for that price these days.
I still have one S2, a black-dial, to go with my SP 2005. It also has the problem. One day I will get it repaired and repainted just for fun.