We started with the same 11-32 cassette you have. I left it on there and sampled what gears we needed for some of the steepest climbs around us before reducing the range. For reference, the low gear on my single is 30/23 and my wife's is 30/27. The low gear on the tandem is 28/28 with a 26" wheel. I don't think we've ever used that gear.

Certainly leave some margin for the epic ride where you've burned out and still want finish! Also (on a single and the tandem), I find I/we need lower gears in the winter, when we're not in as good shape, wearing more clothes, and breathing cold air. Hills we tackle at 42/24 now might be 28/21 in February.

At first I wanted to take off both the 32 and 28 from the cassette, but then under closer consideration, I only removed the 32.

Starting point:
11-13-15 - 17-19-21 - 24-28-32
Remove 2:
11-12-13 - 14-15-17 - 19-21-24
Remove 1:
11-12-13 - 15-17-19 - 21-24-28

The "geometric" spacing of the last option appeals to me. Comparing the second to the third options, you gain the 14 and lose the 28. The 14->15 jump is the smallest ratiometric jump in that whole cassette, and it comes at the price of the 28 tooth bailout gear. I didn't like that tradeoff. On the other hand, adding the 12 is a win: 11->13 is the biggest jump in the original cassette, but high speeds is where you'll want tighter cog spacing. (Same increase in effort leads to a smaller increase in speed due to air resistance.)

With a quad front chainring setup and a 24T small chainring, personally I'd be tempted to go tighter than the 11-28.

Keep in mind that the "franken-cog" setup come at the price of additional wear on the freehub splines; I think TG posted some pictures of amazingly fast wear on an aluminum hub without the cogs pinned together. In order to add that 12, I had to remove the bolts that pinned the larger cogs together.