I come with experience in this, some may disagree with me, but my whole life I have always practiced guitar in front of a computer, thus have used many plug ins. From the time I was barely a teenager with my first guitar port, to now, almost 30 years old with Amplitube 3. I went through many things inbetween.
I have the Pod HD500, the models are more updated than the XT you have. However, it comes nowhere near Amplitube. I am speaking about amplitube on Mac/PC, I also have amplitube on the iPad and honestly it's not that great. Especially if you want to do high gain stuff.
However, Amplitube on the Mac/Pc is impressive. For example, I use the Engl Powerball with an Orange Cab and tube screamer as my main amp on there. For cleans, I use a fender twin. It allows you to buy whatever cabs, mics, and amps you want. They emulate the real amps fairly well. The 5150 on there is good too. I think it sounds better than Peavey's Revalver 5150.
The reason I keep my Pod HD500, is because it works as a Midi Controller to my live rig, AND my amplitube home rig. It allows me to switch channels, use the wah, etc. If your Pod XT has a midi out on it, then keep it, because it'll work with the plug ins. That is all I use it for. I use it with my live rig for the same reason, however I don't use the sounds or effects of the Hd500, but it's a nice midi controller.
If you have a setup with a subwoofer the Amplitube sounds amazing. I use Rokit 6's and a 10 inch, M audio MBX10 subwoofer. So, the guitar sounds amazing through it, as well as bass.
I have no idea why hardware isn't better. Besides the Axe Fx, most hardware isn't that impressive nowadays. I do use a Digitech1101 through a mesa 50/50 live. So I am using a modeling pre amp for a live rig, however it sounds far more realistic than the Hd500, especially through the tubes. Without the tube power amp, the 1101 doesn't sound better than amplitube plugged in direct.
PodFarm does not come close to Amplitube. I know YouTube isn't the best way to judge things, but go check out some Engl Amplitube videos. Whatever it sounds like on YouTube, through your computer speakers/monitors, is probably about what it will sound like when you own the software. Especially if the person has not mixed and mastered it into a song.
You can get the free version to try it out, but it doesn't have any cool amps. If you don't want to pay 300 dollars for the full version, you can just buy the amps that you want. Or you can get special packages. For example, for 99 dollars you can get the metal package, or you can get the fender package, etc. I think it's best to go with the full version and then buy a few extra amps on top of that.
Also, some special packages come with interfaces. Even if you don't need them, might as well get it if it's free. Like Amplitube Metal comes with the i-Rig HD, which plugs into your Mac/PC or iPad.
It comes with the Orange Cab sim, which is the best Cab IR I've ever heard. Even when using other plug ins, or real pre amps, I run it through amplitube and bypass the amp and use that cab. I have downloaded a lot of sims over the years, and that one always sounds the best.