Richard, be very weary of Idealism and Generalism. 90% of businesses fail, very few have exits. If you can raise money now on an idea, more power to you. Do it! The last thing you should be worried about is valuations and what if scenarios that are 5 years down the road and have long shot odds. Hey, if they say the business plan is obsolete once it's written, how can you worry about projections and valuations that look 5 years into the future?
If a couple other vc backed co's are in this already, you'd better get going! If you are worried you are going to waste the money because you can't control a team and project manage a prototype, then you aren't cut out for a Series A round either.
Talk to people who have startups that have raised FF, A, B, and C rounds. You'll hear their stories don't fit a mold, a generality, or an expert's article. there are always nuances and even big strokes of strategy that turn the tide.
Get in. Get Going.