Good advice.
Using an alternate cryptocurrency client would be a great way to get many people to install a hidden virus that targets Bitcoin users.
If you have a significant amount of Bitcoins, I wouldn't run other clients on the same computer until the alternates have developed trust over a longer period of time... I'm probably on the paranoid side of things though.
These new cryptocurrencies are interesting, and it will be fascinating to see how it will all play out.
I think we can´t even say that those precautions make you paranoid, its just being safe. There are so many altcoins being launched, and a LOT of scammers out there... I should be doing as you said: using another computer or maybe in a virtual machine (that may not even be enought) to run for example, a wallet software of some altcoin that i may eventually try. For a matter of lazyness, i am not doing that, but i use to check any file i download with online and offline security tools.