Although you'd never guess it from these posts, there are quite a few people out there who think that having a big traditional wedding (complete with white dress) after having lived together for years is a bit much.
That being said, those usually are the folks whose feelings you would have guessed long before you announced the wedding date. If your friends have never said a negative word about you living with your DFiance and didn't seem to have an issue with that, then I'm a little surprised they said what they did about your dress. The wedding is just around the corner and it's not as if speaking their minds would cause you to run out and purchase another dress, so why even mention it? It was pointless.
A few years ago, a relative got married. Between her and her fiance, they had 5-6 weddings behind them already. Each had 2 or 3 marriages. We'd met the guy a few times and he seemed very nice and we hoped he'd be a keeper.

I'll be honest.....When she pulled out all the stops and had a big*** off-white formal gown in her 40s and it was her 3rd wedding and probably his 3rd or 4th, I thought, "You've got to be kidding me...." But we went and supported them because we really wanted this one to work and as I said, he seemed so sweet.
Not long after the wedding, she was diagnosed with a terminal illness that will result in a slow and gruesome death. Many new husbands would have cut and run when faced with what they were told to expect. But her DH has been one in a million. He has devoted himself to her care and has made sacrifices beyond belief. He is still crazy for her, despite the agony they face every day. Now I'm glad they had the big wedding and she had her fancy, flowing gown. The way she looked that day is a far cry from how she looks now, and they have those lovely photos and memories of that day to cherish. After she's gone, he'll have them to remember her by.
When it's all said and done, it was just a dress.....But it made her happy.