Piston time will count towards those hours needed to keep your license valid though. And if you have someone else pay for them like parachutists, glider pilots or students, this might be helpful to you while you look for that elusive first job.
In the end, it is your choice. You can of course sit and wait for someone to hire you, or pay up for a rating that may or may not be of use to you lateron (what point is there in getting rated on a bus when the first job offer that comes up is on an ATR?), or you can fly whatever you can get your hands on and get a wider experience along the way.