I appreciate that is very difficult to keep these things current when you are having to pay for it yourself with limited funds. However I would advise anybody who can, to keep everything (medical and IR) valid and current.
The temptation is always to cutback wherever possible. The problem is that it doesn't get any easier the longer the period of lapse.
It is all well and good to say "renew when there is a possibility of an interview," the trouble with that is, that the application will almost always want to know the date of your last test.
Companies are not struggling to find applicants. They are looking at whittling down very large piles of applications to arrive at the limited selection of people to offer interviews to. With this in mind, nobody would be doing themselves any favours by not being current in all respects at the point of application.