I don't think the wood Kode 86 is particularly heavy mean weight comes in at 6.2kg and flare 98 wood carbon will not be much lighter. But due to both bigger size, more width and tail width and a flatter rocker, the Flare 98 will fore sure still get going a bit earlier in underpowered 5.4 and regarding jumping ("popping") in such conditions the difference will be even more noticable (in favor of the Flare 98). So if this is something you truly value I think adding a Flare 98 can for sure improve your light wind sailing.
But unfortunately, I doubt you will like it very much for any type of wave sailing (except for pure freestyle sailing in waves). Wave _riding_ will simply be rather bad, far, far from the Kode 86.
I see a few different solutions. Getting a Kode 80 is one, but it's a fairly small 80 liter board and although it has a faster and "crisper" feel to it than your Q71, I don't think it's that much better in light wind wave sailing. It's a board that prefer a bit more power to work its best in wave riding. In that case, I figure keeping the Kode 86 would be better.
Another option is to try to explore the light wind abilities of the Q71 a bit more. It' not a super small board for you and when you get the hang of it I think it can take a 5.4 when it has to. Bit this is a bit borderline, and hence one option would be to ad a powerful 5.0 to your sail quiver. Then you could really take the most out of the light wind abilities of the Q71. 71 liters may sound small, but it is a very wide 71 liter board, with a lot of fin too, so its light wind potential is quite big. It will not give the blasting feel of a Kode 86 (or 80) but its still amazing upwind, rides waves very well and has a very nice "pop" for getting height off small waves due to all that fin drive.
So, depending a bit on the economics, I would first look for a Flare 98. Then experiment more with the Q71 in light wind wave sailing, first with the 5.4 and if that feels awkward, with a powerful 5.0. Depending on how that works, you might then sell off the Kode 86...or keep it if you still like to get back to that blasting feel now and then. In any case, I figure a Kode80 and Q71 in practice are closer than Kode 86 and Flare 98 is.
(I'm about your weight by the way, and have sailed all these boards, except for the latest generation Flare both in waves and on lakes. I did sail the previous Flare though.)