I've got a set of cast rims with the A3's mounted, and my spoked rims with Anakee Wilds. When I'm in the dirt, I want the most dirt-capable tires, because I'm not always riding forest service roads or the like that an 80/20 tire is good for, I'm off road. When I want to go on a long haul touring trip (the bike can do both - so I use it for both), I have the A3's. Which I think I'm going to replace with Road 5's when they wear out.
Got the rims on ebay - bought front rotors from the same and TPMS sensors. Makes for a quick changeover if something 'fun' comes up and I don't have the best tire mounted for it, I can change tires in 15 minutes.
Thinking of offloading my spoked rims for Woody's 21" front and matching rear on SuperLights with Superlaced and Supersized spokes - the BMW rims are... soft. If you want to do it, do it. Just get the parts from a GS and it will bolt onto your GSA. Careful if you take your cast rims on hard off road - they could break, but cast rims will handle gravel and fire trails without much problem (from what I've seen).
It's an expensive bike and an expensive passion, kvetching about $ for top of the line gear or top of the line accessories/parts doesn't make much sense to me, but I've been there where I've had to 'get by' for years. Since I don't need to 'get by' anymore, I buy once, cry once, and enjoy the hell outta what I have, because it's exactly what I want, exactly how I want it, and that is damn satisfying.
Also, could hop on my VFR if I want a shorter/faster/sportier ride. Another bike is always an option