I believe that Bruce Lee's message points at how we behave when we choose to value things. I don't think he is against simply valuing "things" in our mind, because that can be harmless. Bruce is pointing out what we "do" when we value lots of things which is, all that we can to acquire these things that we value. We spend all of our money on them. And if we don't have enough money to get the things we want, we get a bigger or higher paying job (for the money) so we can continue to get more of the things that we value.
For us to acquire things we must compensate the person that we are getting the things from. This means taking the time that exists in our life and using it to work at a job that we probably do not like, so we can get money for the thing. And how does this make us value our self less you ask? Allow me to continue.
We all only have so much time in this life. When we take time from our life to work so we can buy and pay for a mass amount of things, we stop spending time on our self. We stop eating right. We stop sleeping well. We stop visiting nature. We stop working out. We stop spending time with our loved ones and friends all because we don't have the time because we "have" to be at work. We even justify our act of "having" to be at work to our self when we know the truth is that we are going voluntarily on our own because we want money to pay for & buy more things.
There are masses of beautiful and awesome things offered in our society that we can easily become fans of. Some of these things even feel worth the sacrifice of our time from our self to attain it, but in truth it is not. We must monitor the efforts that we expel into having things to assure that we are not allowing the things that we think we own, to own us. -Jermaine Andre'