Re. the perceived quality of current Morgans, it has been my experience so far that my new 2015 GDI is having an oil seal and the light switch replaced under warranty but the general quality in terms of fit and finish plus water tightness is better than my previous 2 cars which were both +4's, a 2009 and a 2011.
IMHO, for what I want from a fun car, the +4 suits me perfectly, I can still loose my licence if I so desire or I can get well over 40mpg if that's what I want, but as with all things, you pays your money and makes your choice.
Good luck with which ever you choose, they are both brilliant cars, it's just that the +4 is better !!!!!!!