Hi - Let me caveat by saying I'm new to detecting, having had an MXT for just a few months before getting a V3. In short, yes it has been worth it, even if I'm not sure that I have found things I wouldn't have found with the MXT...I think I may have dug less trash in getting to those finds! Not to mention every day is more enjoyable now when I hunt, here's why:
1) Wireless headphones - Unless you're a beyond-serious audiophile and are a brilliant detectorist with your grey ghosts or whatever, you will LOVE not being tangled in your cord. The few bugs early on were worked out and a minor mod helps if you have prominent ears.
2) Less noise: As a MXT hunter you are probably used to a lot of chatter. That's great and informative, but I listen to the birds above the threshold now and really relax between signals. The V3 can run as quiet or as chattery as you like. Another point on "less noise" is that you can hunt sans earphones with adjustable volume should you feel like it. Sometimes this is nice if its hot out and nobody is around. Not for the sound-brilliant hunter who needs to really really hear, but fine for me when I'm out looking for pulltabs or whatever.
3) Frequency analysis in pinpoint: Being able to see which frequency is strongest is super informative. I have eliminated many targets using this feature. Many many many. Maybe a few that I shouldn't have, but I'm all but done with big pulltabs and definitely don't dig anymore bottle caps.
4) Dealing with EMI: You can hunt anywhere with the V3, bring down sensitivity and/or switch to 22.5 only and you're good.
5) Dealing with salt: No more trainwreck on the beach with your MXT falsing like mad. Use "salt compensate" and move from wet to dry sand like nothing.
6) Backlit screen: Wow! Hunt at dusk or continue into the night without straining your eyes. So nice you wouldn't believe it. Also switching color scheme can help you deal with super-bright sunlight or any other viewing condition.
7) Maybe should have been listed as #1: Customer service - If you have a problem, these guys will take care of you in a week, less if need be. I've had a couple of replacements needed and a whole detector replaced thanks to these guys and hardly missed out on any hunting time. I probably won't buy another brand of machine.
Flexibility: Even better is that if you keep your MXT as a backup or unit for a friend all of your coils are interchangeable. Sure, perhaps you can't use TX boost on many of the coils you use on your MXT, but in some places, due to the ground, you won't be able to use Tx boost anyway so it may not matter.
If you have enjoyed learning the ins and outs of your MXT you will love the V3. On days when you can't hunt you can hunt in your mind by coming to this forum and others and learning and watching videos. If you have a solid V3 it is both a turn-on-and-go (almost) machine and also a tool with a very long and enjoyable learning curve.
For me its worth it.
The village idiot,
Taterhead