Our new, old bike - Just how green are we cyclists?

The question, as usual with an old bike, becomes ‘how far do you go?' We’ve ridden the bike, it works, it goes and stops, but the handlebar grips and twist shifters are ergonomically heretical, the chainrings look like a circulating shiver of sharks, and the ‘it’s knackered, change everything’ 0.75mm chain wear gauge flaps around in the links of both chains like a drunkard's wotsit in a pub toilet.