If they are trying to get you in a newer machine there is a reason. Changes on machines, especially on "new from the ground up" machines like the JCB are continual. Whether all your issues with your machine have been addressed, is of course unknown. However it certainly will be an improved machine over your current machine.
If JCB is unwilling to help, you are unlikely to get the amount of recourse your looking for, unless your dealer really steps up (and you provided the dealer a very nice profit margin on the orginal sale).
Be diplomatic but you will need to have a "stick" in your hand. That would be informing them of your activity on internet forums, word of mouth and letting them know about the hardship that has been caused by JCB ownership. When all is lost, I have heard of people parking machines at major intersections with signs hanging off of them depicting issues with brand.
I still think JCB will step up if they agree your machine has been a problem. If your dealer is willing to do something for you, I take that as a sign that your dealer agrees with you.
Good luck. Dont let them take too long to get back to you. Every day that they procrastinate the closer your machine is to losing the original warranty period. I think your case is stronger while your machine is under factory warranty.