In regards to "but that wouldnt reflect my earnings.. which post people seem to think it should" - Fuck em, what do they matter anyway? No-one has to justify themselves to anyone!
In regard to buying a flash/nice/fast car - if you are away for 18mths/2yrs at a time, then whats the point? Have this expensive car sat there a) depreciating and b) making an ideal target for theft while you can't drive it!
If cars is your passion, then for sure spend on it - buy a decent car for what you need. Might be nice to have a £40k car sitting there looking flash, but if you can't drive it then why bother? Id' sooner have a £15-£20k car and £20-£25k sat in the bank than a £40k car and worrying about if all the bills will get paid....
Fuck, I ain't even got a car

I'd sooner pay my bills everymonth and have some food to eat than spend out on running and insuring even a poxy 1.1 L reg Fiesta