Depends as does everything. 28 to 32 is still 14% which is the difference between a cadence of 60 and 68 or so. This might be enough for the OP and it's a relatively inexpensive experiment - cassette and chain assuming he has a mid-cage RD.

I'm spending about $400 to convert my Volagi to a triple. I could climb most anything with a 36t in the back and that will be my fall-back for a really ugly ride, but a 30-30 or 30-32 should be fine for almost any 100K at 100'/mile and many Centuries. A triple with a 74mm BCD gives you a 39t chain ring which many find gets heavily used and the ability to put on a true granny.

+1 on the suffering best done under controlled circumstances (training) versus having to suffer the last 30 miles of a Century where that additional, lower gear might save your legs.

OPs don't generally provide enough specificity to really understand their situation so we're all left guessing and suggesting all over the place, such is BF.