I would think the main advantage of Silicon Valley would be access to talent with experience in marketing web-based products. You can hire experienced people without relocating them; there are a lot of marketing and PR firms with a presence there, etc. And don't discount the network effect... in Silicon Valley when you go to pick up your kids at school the other parents there are just as likely to be the marketing manager at SalesForce or the publicist who did the campaign for Netscape, something which never happens in Maine.
In general, the locality benefits of SV are mostly related to prime VCs being located there and a good talent pool.
In theory, if you are a self-funded operation that is fully staffed, you could be located in far north Maine and have as much viability as if you were working out of Facebook's lobby in Palo Alto.
I say in theory, because I think that you can't discount the side effects of just being in the area of SV and overhearing things and being introduced to people.