Is it useful:
Id say it depends on what your aiming for.... if you just have a PPL and are staying with it then if you had a IMC you could fly in more weather conditions
But if your going on your way to get a f/ATPL quite quickly a IR would do the same thing so you would be wasting your time and money on something you could do without
Just my oppinion, im no expert, but it seems logical
Martin