Newkid - yes, in all probability I would eventually get the IR rating, just most likely not straight away. This is mainly as I want to go down the instructing route for a year or two rather than straight into airlines so it doesn't make sense to spend the cash early. However, I do think you're right for the general case as if a chance of employment does come up then you've got to be ready to take it.
The one thing I haven't researched is what is necessary to keep an IR current - does anyone know? The other thing I wonder is if you were say happy to continue instructing for a while and didn't get your IR within the 36 month deadline after ATPL theory, you must still maintain the CPL theory aspect, so how at a later day would you revalidate the ATPL theory - surely you don't have to resit the whole lot again?