Listen to Denverpilot. You will want to train for the IR with the equipment you want to fly with. Today that means WAAS-GPS. Most IFR capable ships today have at least one navcomm with ILS plus WAAS GPS. Many will also have an AP. You can fly IFR with less but why in today's environment, especially if you fly into and out of smaller airports? It will be far cheaper to buy these items pre installed than to put them in yourself, especially in a minimally capable plane (like a 2-seater). It may likely be cost effective to finance a more capable and well equipped plane rather than throw avionics money at a runout.
Consider: A fresh WAAS GPS install will cost a significant fraction of your aircraft value. And these things multiply. You may find your audio panel and blind encoder is not compatible with newer equipment, etc. etc. Long term owners know this, because we've been through it and written the checks.