I feel like each instrument I want to own should be justified in some way. I still have my great grandfather's violin even though I haven't played it in years, but it is justified by that connection. I have some GAS for two basses right now that would meet very different needs, and I feel like that is justified as well.
If you don't need to downsize/thin the herd, then take some time to think about the gear you have, why you have it, and why you should/shouldn't sell it. If you are honest with yourself you will likely arrive at the best decision. If you do need to purge for other reasons, (often unexpected financial situations) but you have decided that the instruments you currently have are justified and you do not wish to part with them, then you will have some tough decisions to make. Chances are if your instruments are that important to you, then there are other ways to get out of your financial situation. At that point, you have to ask yourself what really matters in your life, and act accordingly.
That's where my head is at.