Don't forget that one of the Almaz station did test fire an aircraft machine gun in orbit. Short of deploying an operational system the implications of space weapons testing in and of itself aren't very big.
If we get into a TL where Polyus is actually deployed Star Wars becomes almost a given, and between the two programs things are going to be drastically different, and in unpredictable ways IMO. Most obviously this is going to hurt the Soviet economy in a big way; you either need them to have more resources, make big cuts elsewhere or this is just going to hasten their decline. In terms of the Americans Star Wars will IMO probably retard more conventional military aerospace quite a bit. Things like the F-22, F-35, V-22 etc are going to be very vulnerable given the cost of Star Wars. On the other hand new space probably gets started a lot earlier and there is a very good chance that a space shuttle replacement will come online around the turn of the century and that launch costs are significantly reduced even if the SSTO's never really perform as advertised. Space militarization is going to happen at this point, and you are going to see more and more weapons platforms based on orbit. Anti sat missiles will be a big deal inevitably, and you will probably see a lot more countries working on an indigenous launch capability.
How this all shakes out is a big question. I wonder if it may not prove to be mostly a big expenditure in the 90s and early 2000s that hurts more conventional military readiness. Once the Soviet Union breaks up there is going to be much less obvious need for something like SDI. The end result might just be a boost to space capabilities at the expense of OTL aerospace. Frankly I think the 'destabilizing' potential of missile shields, working or not (and I don't see how any of these systems could have approached fully functional any time before the Soviet collapse) is seriously overblown - nukes are nukes countries are not going to start throwing these things around just because there's some (largely untested) capability to intercept incoming ICBMs.