If not I'm probably better off getting them anyways to cover myself for any digital shoots.
As Mr Mullen said IRND are almost never used when shooting film. As for digital, I wouldn't necessarily just get IRND's, it really depends on the camera you choose.
Nowadays, most pro super35 cameras either got internal ND's (Sony F5/F55/FS7, Canon C300/C500, Arri Amira and more) and some like the RED Dragon don't need IRND's. Also some that does, like the Alexa (at least older models) you could use IR cut off filter on top of normal ND's if I'm not mistaken.
That leaves us mainly with Blackmagic Cameras and some DSLR cameras and even then mainly when using ND's over 0.9 or even 1.2 depends on the camera really.
So the main question would be, do you want it for General purpose use or for a specific camera?
If General, I'll actually think if you really need more then one or two ND's and probably go for normal once not IR as a long time investment.
Also, because Many cameras today already have internal ND's I would consider to get some ND's plus one or two Soft FX filters or similar that cut out some of digital edge from the image, that could actually be more useful.
So for example getting: ND 0.6+1.2+Soft FX 1 or 0.6 +0.9+IR cut off+Black Promist etc etc)
Hope this helps.