My personal opinion. Please do not think or assume the 34461A is bad device, for $800 shipped is a good deal go for it if you need one!
Agreed that having the schematics is a big point in the 34410A's favor. And while the fan noise was obnoxious, it is easy enough to fix by adding a Zener in series. It doesn't need to move anywhere near as much air as it does, when operated in a normal lab environment.
Boot time was annoying when the 34461A first came out, but it was improved significantly with firmware updates. It now takes less than 30 seconds, which is fine. It powers up when I flip the switch on my workbench every morning and goes off again when I leave at night, so I don't much care how long it takes to boot.
I'm kind of surprised at how long it's tolerated that treatment, frankly -- at least 10 years, day in and day out. If/when it dies, it will almost certainly be replaced by another one from the same series.