i would say that you should keep it road legal if that is where you enjoy driving it.
I keep contemplating taking mine off the road, as the tuning side has not exactly been 'smooth' so far. But, every single time i get it running right for a few weeks or a month, it puts such a massive grin on my face that i know i would miss not driving it day to day.
Although i have kinda thought about buying a ZT 260 for a 'sensible' tow car - get it supercharged and then have a heart attack every time i take it out and it drinks fuel like mine drinks coolant
that said, mine has done 11K miles since last MOT, so says a lot about the reliability of the L-series, that even with a HGF it can eat up the miles without any adverse issues!