Hello and welcome to TST. What one may gain from updating clubs can vastly vary. Club head technology has certainly improved with the ability to get the ball in the air and to be a bit more forgiving than older models. The shaft plays a very important role as well, maybe even more important which is why a fitting can be very beneficial. As far as expectations…hard to say. But at the very least you’ll know you’re optimizing one area of your game by having the best irons for you. Cheers.
Unless you have undergone swing changes I wouldn't expect any change at all.
The lofts might be stronger which could make you think you've gained distance when you haven't.
10 year old cavity back irons of good quality aren't much different from brand new ones.
Your golf doesn't improve when you get new irons unless you were playing something with the wrong shaft or clubs with little or no built-in forgiveness.