When I go out with the missionaries, I rarely wear a suit and tie. Instead, I usually opt for trousers and a causal shirt.
This might be completely unsurprising for many people but it has recently come to my attention that, in general (just like when they go home teaching), members will very often wear their Sunday best when they teach with the missionaries. While I do not have strong feelings either way, my preference for something causal is principally motivated by the fact that Mormons are often perceived as weird. Wearing something smart but informal hopefully signals that not all Mormons wear dark, ill-fitting suits, hence reducing the weird-factor. Too much formality could also be a barrier to a spiritual conversation, especially if three men in suits are visiting a single women.
Clothing is clearly an important symbol of worship and sacred space. Hence I usually try to dress more formally at least some of the time while home teaching. But such symbols only work when they are known and understood. Those just learning about the church are unaware of the significance of such symbols and so wearing a suit and tie will be meaningless to them.
Does anyone else still wear a suit and tie?