You know...
Even though it has a rounded top, that doesn't mean you can't add toys

I have flat top cages that open up at the top, but I never use the feature. So what I did was put a forked perch (has two or more branches on it) so that it is pointing straight up in the air and then I attached some toys to it. Max loves playing up there!!
Also, I've attached a long birdie boing to the ceiling (using one of those plant hooks) and have it so that it circles down towards the cage and then I attached whole bunch of toys to that! (using zip ties and other safe stuff).
Here is a picture:

Now, it looks like the birdie boing is far away from Max's cage, but it's not. It is pretty close to it...
(Max asks you to please excuse her house, as this was taken prior to cage cleaning day

)

So you see? You can get rather inventive

I don't use play stands/gyms for any of my birds. They all have a birdie boing above their cages and it's loaded with some cool toys.