Only you can decide whether or not to continue you with your application. I will say that I know several people like you who have had very little medical input over a number of years (even decades) and it has not stopped them making a successful PIP application.
BIS
Just an update that I did pull my claim before the return extension. I had the form ready to go and sealed but couldn't face the thought of justifying myself in assessment (with visual inspection of the outside by someone I'd have no confidence in to make a judgement) so didn't send it and there it now sits in my filing cabinet. I've had the DWP letter saying benefit stopped and the package from Motability to inform that my worry free days of getting around are at an end in a few weeks. All rather depressing stuff as I'm sure that most are aware of anyway