I sometimes wonder why people get so hung up on bases....add a little this....a little that....maybe a parsnip....boil it for an hour....three hours....oops! don't forget half a carrot..... A base is a base; and should provide texture and a background flavour. No more and no less. Lots of onions and some light spicing is the trick.
As Andrew says, most of the flavour in a finished curry will come from the final spicing, and reduction, in my humble opinion.