Realty, as someone who used to buy various concert and sporting events tickets from brokers who has now converted almost exclusively to scalpers, I had to chime in on this one.
Based on my experience, no, a broker will not back off of their price 30 mins before game time if you call them. In fact, if you call them during game time, they won't back off. This is because many of them send "representatives" <cough> scalpers <cough> down to the venue to unload any tickets they are stuck with at event time.
That being said, you can definitely purchase tickets for face and sometimes below face for Laker games from scalpers. I haven't done it in a few years as I am a season ticket holder and now being gouged by the Laker organization and NBA directly. But I go to about 20 games a year and I am constantly talking with scalpers as I walk in to see what tix are trading at. As I mentioned above, virtually all of the scalpers that you encounter at any venue in LA, are "contracted" by the brokerages to unload the tix they are stuck with at event time. Obviously, if the event is already underway (e.g. it's 8:00 and the tip off was 20 mins ago) you as a buyer have a lot more leverage. And brokers would rather take something than nothing, but they aren't going to do it if you call them directly for the reasons you touch on in your post. I'd have to think a Lakers/Spurs game would be tough because there are so many "suits" that will buy tickets from brokers and/or scalpers at a marked up price to take clients, etc. You're better off going to a "less desirable" game. Of course, over the past two seasons, there are no longer any "gimmies" for the Lake-show. Of all of the events in town, the Lakers have the highest demand, so it is tough to get any huge "deals" scalping at Laker games. I think you're hard pressed to scalp 100-level seats with a face of $185 for much less. Maybe you get them for $150. All of that being said, you can definitely scalp tix for less than face at many laker games. How much less, I don't know, but you have to negotiate hard and be willing to walk away from the scalper. As the clock keeps ticking, they get more and more desperate. Even if you pay face value of the ticket from a scalper, you are getting a bargain compared to what a broker would sell the same ticket directly.