Quote Jack Ruston:
I totally agree with Bob. Simulated guitar sounds are terrible to mix.
You're not agreeing with Bob though, Bob's comments were made 10 years ago, on 1st generation modelling hardware, so you're comparing apples with oranges.
There are plenty of commercial releases that show that these guitar plug-ins work, and do sound good, as well as the plethora of YouTube demos by both professionals and home enthusiasts alike, so the notion that they're simply "usable" is, quite frankly, laughable. For the record, I have Twin, a Bassman and an Orange Thunderverb amongst other amps, so I know what a great sound is, and, I'm not biased towards plug-ins either.