I've always felt a lifeline was there for two reasons:
First, to nudge the back of your leg and remind you "Hey dummy, you're about to step off the boat!". Taller or shorter won't affect that gentle reminder, 30" tall might just make it tall enough to tear at belts and pockets. And if you're loading or unloading the boat, the damned things just get in the way, taller gets in the way more.
Second, so you've got something to grab while you are about to ROLL off the deck, or lying on the deck, or seated on the deck. In which case 24" is still plenty tall enough to do the job.
Any way you could just install something else--inboard--to grab or assist in the lunge in/out of the cockpit?
If you want a cheap trial of taller stanchions, stop at the hardware store, get some 1/2" PVC pipe, cut it up into 30" lengths, and tie them to the stanchions on one side of the boat. See how you like that, before you invest in stainless. Shouldn't cost you more than $5-6 for six pieces that way.