I installed the ARP, the CS80 and the MiniMg over the demo versions on a PC running Windows XP.
They installed perfectly well, but I did have to reinstall the ARP and the MiniMg because they had a tendency to freeze. I suspect that was due to a soundcard change, though. But the soundcard change didn't affect the CS80 or the Mg Modular that I'd previously installed. It may be that the ARP and MiniMg are more delicate in that respect.
Based on that experience I'd say either delete the demo or else reinstall if you do encounter problems later. The reinstall procedure was very smooth and easy, BTW, and reinstalling the patches I'd created was so easy that at first I didn't realise I'd done it and I was looking for the next step.
Like you, I was a bit wary, but everything went so easily that I needn't have worrried.