I think a good motivational feature of Garmin Connect, on top of your own personal goals, would be to unlock awards for reaching certain milestones in your training, whether that be running, cycling, or other Connect compatible sports. Take running for example. Awards could automatically be given for things like completing your first 5 miles in one go, right up to things like successfully completing a marathon or even an ultramarathon, making sure that everyone at every level always has something to inspire them when they train. Similar awards could be given for completing cycling based achievements. Awards for tallied distance totals would also inspire people and motivate them to go out and train, thus making every session count. Awards that are given for reaching time/speed milestones in each sport would add an exciting element to any training session, and could potentially reveal undiscovered future talent. There are lots of ways that this could be implemented alongside (not instead of) the personal goal system, and would ensure that everyone had something to aim for.
Andrew