I've noticed that in Silicon Valley, angel investing seems to have much more of a status aspect than elsewhere. Angel investors are "cool" and people will admire you during parties and whatnot. A FB engineer striking it big and starting to angel invest should be seen as a "nouveau riche buying status" move and not necessarily as a means to gain even more money (though that may be a welcome bonus of course).

The status aspect is largely missing in other areas of the world and may be one of the reasons why finding investment in SV is so much different than elsewhere.

The general rule is that you don't divest yourself of an asset unless you are going to buy another asset or make an investment that better serves your financial goals. Cash is just money, but equity will work for you 24/7/365 for as long as you let it. Everyone has different circumstances and preferences though, so there's no universal answer.