I’ve used both the Arc 5 and the Braun Series 9 Pro Plus, so thought I'd chime in. The Arc 5 LV-65S is a solid shaver, and I found it great for both dry and wet shaving. If you're thinking about replacing the foil and blades, the newer replacement blades are indeed more comfortable and can give your shaver a bit of a refresh.
Now, regarding the Braun Series 9 Pro Plus, I made the switch myself and was pretty impressed. The Series 9 Pro Plus gives a really close and smooth shave, and it’s gentle on the skin. It's also quite good for both dry and wet shaving, just like the Arc 5. One thing I noticed is that the Braun handles thicker growth a bit better and is slightly more comfortable over longer sessions.
Since cost isn't a big concern for you, the Braun Series 9 Pro Plus could be a great upgrade. It’s a bit of an investment, but in my experience, it's worth it for the comfort and performance. If you do decide to get the new shaver, you probably won’t regret it. But if you're happy with the Arc 5, getting the newer replacement blades can definitely give you a nice improvement without having to buy a whole new shaver.
Hope this helps!
Rodney