Nobody knows if it's only the high-end Vegas, that's an assumption. Having more data helps you make a better decision. For example, you haven't told us anything about your situation other than that you are putting together a Ryzen 1700 system. You haven't said whether or not you're only gaming, playing at 1080p 60hz, 144hz, 1440p, or might go 4k someday. You haven't told us your financial condition such that we know what money's real value to you might be. $50 to me isn't a big deal, but to you it could be.
Consider that Vega is the first real architecture change for AMD on the graphics card side of things since the first Graphics Core Next (GCN) GPUs came out. They are going to a tile based rendering system that has proven so effective for NVidia these last four or so years. If AMD has made any real significant progress, such that their own products eclipse the Polaris GPUs, you could see the RX480 dropped to a much lower tier in their lineup. Whether this will happen I don't know, but waiting some period of time for the information could be worthwhile to you.
Also, if all you plan to do is game, you could wait for the R5 chips to come out and perhaps save enough money to get a more middle tier Vega. Ask yourself, do you think a 6 core Ryzen with a GTX1070 would outperform an 8 core Ryzen with an RX480 for the same price in gaming applications? I certainly think so. There's probably an 18 months lifespan difference between those systems. If you were to swap the GPU in the future, the 8 core system would be the better way to go today.
Even if you were to just get the Asus 480, you'd have quite a solid gaming machine and probably be very happy. My bet is AMD isn't going to outright discontinue the Polaris series, and it may not even get much of a price drop if recent trends continue, but a couple of months of waiting to know would be worth it to me if I want my purchase to last five years.
You didn't get an answer in the other thread because people are hesitant to answer a question without knowing enough data to form a solid opinion.