Answer: Surprisingly, no.
To review, last December I purchased three identical Wacoal bras that I washed by hand with different cleansers. On Bra 1, I used Tide; on Bra 2, Le Blanc; and on Bra 3, Forever New. After wearing and washing the bras for seven months, I then (A) asked others for their opinion, (B) lined the bras up against each other, and (C) lined them up against a new Wacoal bra in the same style and size at Macy’s.
There was a slight difference amongst the bras. Everyone agreed that Bra 1 came out looking the newest, followed by Bra 3, and finally Bra 2. However, the difference in stretch between Bras 1 and 2 was only about 3/16ths of an inch. The difference between Bra 1 and the new Macy’s bra was also about 3/16ths of an inch (which makes the difference between Bra 2 and the Macy’s bra about 3/8ths of an inch). There is a possibility that I could have worn Bra 2 more than the others–it definitely looks that way.
My conclusion? The only reasons to use a special lingerie wash are if you (A) really like the scent (and I love both the Le Blanc and Forever New scents); and (B) you get tired of trekking to the laundry room for that big heavy bottle of detergent–you can more easily store Le Blanc or Forever New in your bathroom.
One more thing I learned: I don’t need to replace my bras every six months. However, it’s a good idea to go into a department or lingerie store for a tune-up. Compare the wear, tear and stretch of your current bras to a new one to see if you need to replace them or just tighten the hooks.