well no-one would embark on a project and tune a diesel to more than the factory limits now would they *cough cough*
Don't get me wrong, there is throwing good money after bad if the research and the development has been done, but if there are still unknown's then people will always push the boundaries, whether it is 'sensible' or not.
the L-series for example, put in a set of the SDI's and get it remapped, and leave everything else as it is, and you increase performance and factory figures by about 40-50%... that is cheap as chip it is only when you wanted to go further does things start to cost... as we have all discovered.... and that should now be less as some of us have worked out the failure points\reasons now for the benefit of the 'many'
If mods are not declared then they are stupid though i agree but declaring mods isn't that expensive now as lots of brokers provide cover for it now - my ZS is only £500 a year insurance in Bristol in BS6* currently with all mods replaced like for like,fully comp, protected no claims, commuting, 12k miles etc (*quite a high risk postcode even if the area i lived in wasn't)..... My 1.4 58 plate fiesta zetec with 8k annual miles, mirrored no claims no mods is £370....
As to whether i would make the same mods to my car a second time, the answer is of course no... if i had a crystal ball, and spotted the headlift due to a poorly spec'd turbo sold without any real testing having been done on it - i would have stayed well clear!
But I might have gone down the twin turbo route instead for a fraction of the cost i spent working out those issues and blown it up in a different way
Oh and for some it is the challenge that makes it worth while... i know some-one that used the manual injection pump, normally only good for 85bhp and got it to spit out dam near 140 or thereabouts...
not sure if the above means i am old or young, but at 31 i am now a lot wiser than i was when i started the project regardless
!