Insofar as coriander is concerned, cut it back. I have seen this grown commercially, and the farmer takes several cuts of the upper leaves during the season.
You may want to allow the coriander to go to seed, as it is an annual and the seed is probably used more than the leaf is. You could grind up the seeds to add some spice to cooking.
I have just realised that my coriander (widow box) has flowered (three pots, rosemary, thyme and coriander) so now I'm really interested in the replies and apologise for my frivolous answers.
It appears that the basil can be a perennial or an annual variety (just looked it up) but in any case in the relatively cool UK climate it's treated as an annual, as that's how it will behave here.
I'm guessing that yuo will get a longer life out of the basil if you nip the flowers out.
Curry evenings sound great! you've got my gastric juices flowing now ;-)