I found that purchasing a nice bike made riding much more enjoyable for me (and, thus, motivated me to ride more) because the improvement in ride quality compared to my former bike - a 9-year old hybrid - was huge. Riding more, in turn, has resulted in substantial improvement in my health. Thus, it was all worth it to me. That being said, if you don't think buying a new bike will be a material improvement over your current ride, just save the money for buying the accessories you want to buy or treat yourself to a nice trip with your bike. It's a win-win either way.