Just for clarity, your line should be capable of a faster connection right now, but it looks like your earlier problems have caused your SNR target to be raised, that is why your sync is as low as it is.
If that problem was removed you'd have a faster connection on ADSL but even then going to ADSL2+ would not make much of a difference.
If your attenuation was lower then there would be an advantage in ADSL2+ but unless the internal wiring in your house is really poor I doubt you can do much about the attenuation. You can try plugging into the test socket behind the master socket face plate to see if that changes the attenuation but if not then you are pretty much stuck with that.
If your line is a lot more stable than it was you could try to get your ISP to request a reduction in the SNR target but that isn't easy to achieve with a lot of ISPs.