Will the modeling amplifier do more things than my POD will, or is the same thing in amplifier form?

Dunno, he hasn't got one of those POD units and neither of us have played with one. So neither of us has a comparison on which to base an answer. You'll have to look at the specs at the Line6 site and see if you can glean the information that way.

And of the two (Line6 vs Roland), which has the better guitar modeling, since that's what I'm mainly interested in?

Not sure, since he's never tried using the Variaxe in a recording situation. He has told me that in his current recording project, he's sometimes using the V-guitar's modeling, and sometimes using the Line6 amp modeling with a regular guitar, depending on the recording situation. Each one has its strengths and weaknesses.

The last thing is how does the Variaxe play as a guitar?

Neither of us has spent any time playing one, so neither of us is qualified to answer that. I will say this... Never buy a guitar sight unseen. Always sit down and play it yourself. It's very much like test driving a car. You'll either fall in love with it, or there's going to be something specific that bugs the living shit out of you, and you won't know until you actually play it. The only exception to this rule I can think of is with companies like Musician's Friend who (if I recall correctly) let you buy an instrument online and then return it if you don't like it. But that's a lot of hassle compared to just finding the nearest Guitar Center outlet and driving to it.

Oh, and I'm very proud to say that the Line 6 models the Martin D-28

Don't get your hopes up. Now, I've never heard the variaxe's acoustic modeling, but I have to say that I haven't yet heard a modeling system that modeled an acoustic well enough to pass as "real". The modeling systems I've heard all do a fantastic job of turning an electric into another electric but when they try to model an acoustic using electric strings/body, they end up sounding like a piezo-pickup acoustic/electric. There's sort of a "quack" sound to the tone of acoustics that are amplified with a piezo pickup which is very distinctive. You can hear it in many live performances that involve acoustic guitars, and I admit that some guitarists like that sound. But it doesn't ever sound natural. It never sounds like an acoustic that's been well-mic'd with real condenser microphones.

In fact, not even with an acoustic guitar can you get a natural sound out of a pickup. Only very recently has there been an acoustic guitar that sounds natural when directly amplified: the new line of Taylor acoustics with their new "expression system". That one you can plug the guitar straight into the PA and it sounds jaw-droppingly good, without the slightest hint of piezo "quack". But that only came out last year. I bought my new Taylor just as the expression system was coming out, and I didn't know about it until after it was a done deal. Fortunately, if I ever decide to upgrade, my Taylor is one of the models that can be retrofitted with an expression system, so that's always an option for me.

So if you're planning on getting a Variaxe or a Roland system with the sole purpose of emulating an acoustic sound, then definitely arrange to spend time actually messing with it and hearing it in person before making a purchase decision.