I think it depends on how often you want to go flying. I believe that as a basic PPL you cannot take off or land if the visibilty is less than 3 km. If you had an IMC rating this is reduced to 1.8 km. Also, if you were needing to fly SVFR the minimum visibility is 10km for basic PPL but with IMC this is reduced to 3km.
If you find that visibility is one of the main reasons that you sometimes don't get to fly then it may well be worth considering. Don't forget though, if you hire aircraft and find that you often can't get an aircraft when you would ideally like it, if on a particular day the conditions are IMC, any pilots that have booked a plane who do not have the IMC rating won't be able to fly. That may make an aircraft available to you that without the rating you would not even be able to consider flying.
I also think you get to fly instrument approaches as well but the decision height is much greater than for a full instrument rating. Having said that, as I stated earlier, even with an IMC rating the take off/ landing visibility has to be 1.8km minimum anyway. But at least you should be able to line up before you have even seen the runway. I think it is something everybody should take because you may need the skills it teaches when you least expect it. Weather forecast aren't always correct are they? It may very well be 16.5 (or however many it is ) hours of training that save your life.
I for one will take it. Someday.
