While visiting my brother a few weeks back, it was a very, very hot day. I parked on his driveway, and without thinking, left my bike there without using my disc (I was hot, and just wanted to get inside to the air conditioning!) I came out hours later, and noticed my GL1500 leaning over at a precarious angle. To my horror, my sidestand had created a giant pit in the middle of his driveway!
The problem is the narrow little foot on our sidestand - it doesn't provide much surface area for our large, heavy bikes:
I decided to do something about it, and that something is this Rivco pad. They make a version for the GL1500, part number GL15013, as well as a GL1800 version, part number GL18013.
The pad is CNC milled from a solid billet of aluminum. The bottom of the pad is smooth and anodized black.
On the side is a set screw that securely fastens it to your existing kickstand.
According to the instructions, some sidestands have molding flashing that needs to be ground off the bottom. Not mine - and likely not yours either, if you've been riding it for any amount of time.
Backing out the set screw, I realized they had put some sealant on it to prevent it from backing out - and I managed to ruin it by pulling it out too far.
No problem, I had some thread locker on hand. I used removable thread locker rather than permanent, in case I needed to remove it in future for any reason.
A little bit of thread locker on the set screw...
...and I screwed it in tight. It works very well, more than doubling the surface area of the sidestand, and obviating the need for a plate. As an added bonus, it lifts the sidestand by about 1/4", making the bike site up slightly straighter. With my Austone Taxi Tire, which is slightly taller than normal tires, this helps greatly to prevent the bike from leaning too far on the sidestand.
I did have a worry about it hitting the bike when retracted, but I needn't have worried. It flips right up and has more than adequate clearance. I was unable to get it to hit the bike. It also does not interfere with my foot on the footpeg, or with shifting.
Overall I'm happy with this accessory - it's a simple, elegant solution to a problem we all have now and then.
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I'm wondering how universal the fit is, as I'd definitely consider one for my '78 GL1000. Maybe you can straighten me out here.
This thing is CNC milled out of a solid chunk of aluminum. You'd have trouble getting a plastic one strong enough to hold up the bike on soft ground. And 3D printers that print aluminum...well, they cost more than your house. 
