So far, all I've seen is sometimes having "BONUS!" appear when my retainer brings back a crafting material on a quick venture. Instead of getting one NQ or HQ, I get two HQ. Not especially impressive when HQ on normal crafting materials is useless thanks to the crafting nerfs so those materials don't sell for anymore than NQ materials.

I haven't tried the normal Hunting/Botany/Mining/Fishing ventures yet.

I'm not seeing any yield increases on the 18 hours ventures but then I've only had 7 completed so far.

I'm sure there's a point where "better gear" is effectively capped for the expansion and going beyond that won't make much of a difference, if any.

If your goal is to be making more gil on the MB from crafting materials brought back from retainer ventures, I don't think the increased yield/better chance of HQ will work out for you in the long run. It's just going to further saturate the market with the items, driving prices down.

Example: The first thing I got off a retainer this morning was a Stuffed Alpha. Going MB rate at that time was just over 300k, and sales history had shown it to be a pretty steady price over the last 3 months. Twelve hours later, they were down to under 40k gil because so many had come back from ventures today.