I’d stay with the Pi.
Moving to different HW will result in quite a lot of cost and efforts, PLUS you would be sort of getting off-mainstream (important to have as many people to have the same setup as you do when it comes to solving server/OS related problems).
Given you already run a RaZberry board that cannot be reused on any box with USB, new server HW would require changing your ZWave network over to another controller, quite likely you would need to rebuild all of your ZWave network.
Raspis CAN be tweaked to withstand that. See this post.