It should run fine as, like you say, that's how it's designed to work. However it's a vintage piece of computing that's no doubt busted a gut time and time again so giving it a little helping hand to keep cool certainly won't do it any harm

I'd have a look at the surge suppressor and see if there's anything you can do to quieten that down (maybe a quick clean and/or re-lube of the fan bearings/sleeve might work wonders). If you're running the Plus in a well ventilated room anyway (and you can live with the risk of 'surges') then you should be fine to ditch it and go back to the sanity of silence. If it's really noisy though and you still want to try to cool things down, you should be able to hook up a more modern (i.e. quieter) fan, possibly inside the case to keep things neat and tidy