The other problem with valuing ideas is that you can't talk about them without giving them up -- which means you have to say "my idea," "my great idea," "my best idea ever," etc. Teams you can talk about make a better story than startups you can't.
a trusted team will also help establish the value in an idea which is hard to do (in a way others will understand) by oneself. the sounding board can be really useful in helping define the exciting parts of an idea and at the same time distill the competitive bits - which means when it comes time to share the idea with a wider audience, it's clear how far the conversation can go.