Personally? I think don't waste money on two dresses unless you have a traditional reason to do so (ie. your culture wears different dresses or your family does it that way etc).
You said that it's other people's opinions that are making you question your choice, but it's YOUR wedding not theirs. If that's the dress that 'sings' to you and it suits your theme then I say go with it.
My dress was very expensive but very 'plain' according to a lot of people. I saw that as them simply not realising that the simplicity of it was what attracted me to it. It was perfect for me and my expectations so I didn't bend to what they thought and on the day when everyone saw the dress, jewellery, hair and makeup etc all together they all agreed that I'd made the right choice .
I wanted to look like me on my wedding day, not someone else's idea of what I should look like .
Not to mention the idea of disappearing to change to a more 'dramatic' and structured dress seems a bit weird. I mean, by the reception most women are dying to get into something more comfortable, not the other way around lol. I know I was!