My experience with is with my Polo but it should be relevant.

After installing a suspension kit, I found the ride too firm for daily use so I went from 195/55R15 down to 175/65R14 with a huge improvement. Going from a 40 series to 45 won't have as much effect but it should still take the edge off sharp bumps and holes.

I'd still check if you can find a 16" rim that you like which will fit over the brakes. That certainly would noticable.

Fully agree about the tyre cost effect too (yet another reason not to go for big wheels...)