If 30T is "almost" low enough, 32T will make a difference. 1/15 or 6-2/3%.
About the same as going from a 15 to 16T cog on the back.

I LOVE close ratios.
Work out the percentages 2T at the top is mathematically about the same as 4T at the bottom.
However, it doesn't work out that way in reality, because you are moving faster and wind resistance has entered into the picture.
You should also learn your "ideal" cadence and 1T steps at the top end will make more sense.
I typically run 12-23 or 13-25 9 speed cassettes.