Most definitely get the IFR certificate. I had a great instructor for that and to me, personally, it is my favorite type of flying. The first time you hit actual IMC you're just stoked since before that the closest you could get was 500 feet. :P

Seriously though, it will make you a much better and safer pilot. After obtaining my PPL I didn't exactly feel the most comfortable with knowing I could just hop in an aircraft and take off but after obtaining the instrument rating your confidence/flying ability increases a lot.