It's not BS mind you, there's been a lot of discussion.
Now I believe things should be put in perspective. Every new device has some little flaws, and the original XD had some. Updates from GPD ans later LegacyROM turned it into a really great device. Now the XD+ sports some major changes: totally different chipset, Android 7. It's pretty much a new device under the hood, so some issues are to be expected.
I own both the XD and XD+. From what I understand there are issues with the video driver on the XD+ that make the framerate unusable with some emulators. Personnally I have grown fond of my XD+. The only things broken for me are the Saturn emulation (no too big a deal as it's not a system I emulate so often) and some native titles that won't work on Android 7 (or rather with the ART virtual machine) such as Chaos Rings. I have not experienced framerate issues with my emulators (I use RetroArch and Mupen64 FZ 99% of the time) at all.
Otherwise I find that the increase in performance, while not stellar, is noticeable. For instance I have absolutely zero slowdown on PS1, and I can use more complex shaders in RetroArch. Also I have great performance in Mupen64 with crisp graphics: native resolution rendering was a no go on the XD. Lastly some native games such as Star Wars Kotor that used to lag a bit on the XD are much more fluid on the XD+. I also find that the XD+ screen is better than the previous one, brighter and more contrasted.
So I'd say that the small issues are nitpicks compared to the advantages. At least for my usage.The only issue I find annoying is that bluetooth audio lags, it's completely unusable. But BT audio is a hit-and-miss on Android in my experience. I understand that Android 8 has much better BT implementation, especially the ability to use better codecs.
So, to summarize, if you already own an XD, whether or not to upgrade is subject to some thinking. If you're willing to get an up-to-date Android based console, I'd recommend going for the XD+, especially since custom development has already started.