I think the extra reserve power will be more useful than the boots, practically speaking, but I'll leave it to the twin pilots in the forum to give a more authoritative response.
In general terms, you can't/shouldn't fly any piston plane in SLD icing (freezing rain or freezing drizzle, typically ahead of a warm front) with or without boots, so they won't help improve your dispatch rate there.
In VMC, you don't need boots regardless (unless there's that freezing precip falling from above, then, again, you won't want to fly even with boots).
If there's mid-level scattered-to-broken stratocumulus, which is typically 2–4,000 ft thick and can contain SSD (light to moderate rime), you might feel more confident with boots, even though often there won't be enough accumulation to matter. The alternative, for those of us without FIKI, is to just accept a bit of light rime for a few minutes passing through, or look for a hole to climb above into the clear (you don't want to do this if you're going to end up between layers, because the gap can close up on you).
If you fly around in the lee of the Great Lakes much and need to overfly lake-effect weather (e.g. around KART or KSYR) — which typically tops out around 7,000 to 8,000 ft, and contains moderate to severe icing with clear skies above — you'll have the extra security of knowing that if you're forced to descend into it (you wouldn't go in on purpose in a piston plane, even with FIKI), you will be able to handle the ice a lot better on your way down to the emergency landing with the boots. Maybe that would be the biggest benefit.
Pretty wishy-washy, I know, but that's what I have to offer, as a pilot without FIKI experience, but with 17½ years IFR experience around ice in the Ontario/Quebec/New England region. The best winter IFR safety feature, with or without boots, is probably a credit card and a hotel-booking app on your phone.
