Not that he was a reference on best practices, but Mike Elliot/Counterpoint used to do this kind of shit all the time on mods with 500V BlackGates and Cerafines, only they were just adhered to the board with clear silicone RTV. At least these look like they are secured with tie wraps. I don't really see a problem with that. With this case and amp, I wouldn't want the caps sticking out the top for aesthetic reasons.
The input wiring and ac wiring with uninsulated spades should definitely be addressed though IMO.