The other day I was playing around with some planets to see if the numbers for spending, production, and time to completion matched up. It turns out that the time to completion for planetary improvements is a little screwy, but that's the subject for another post, which I'll put up after I've had time to crunch the numbers some more. In the meantime, I thought it was interesting that the "Spending" number on the planet screen (below "income" and above "maintenance") actually includes the maintenance costs, but not the money spent on bonus research and production.
An example - for the purposes of my testing I had set the spending slider to 50% social 50% military 0% research. My planet Toria had the civ cap and three factories and 12 points of asteroid production. That gives me 24 + 6*3 + 12 = 54 total industry points. I had 30% military and social production bonuses (civ wide) and no power plants, manufacturing capitals, or econ starbases. So I was getting 35 (27 + 27*.3) military and 35 social production points on the planet. All well and good. Maintenance was something like 5bc per turn (I forget exactly what, but something like that). So I was surprised that "spending" was 59bc/turn. I had 27 social base + 8 bonus, for which I had to pay 1/2 (4bc/turn), so social should be 31 and military the same. 31+31 = 62. Where was 59bc/turn coming from? Well, looking at some other planets I determined that it was the base social and military production (27+27) plus the planet maintenance (5bc/turn). So there you get 59bc/turn.

So it turns out that bonus production/research costs are not figured into the planetary spending number. They appear all lumped together on the "economic" tab as "bonus production." Interesting point - I was totally up the bonus production and research for my 5 planets, and I was coming up with a number higher than the bonus production costs on the econ tab. What was going on? I figured out that bonus production costs round down and are figured planet by planet. And if you have planet producing one bonus research point (for example) it will round down to nothing. This rounding down is separated out by production type, too, so that if you have one bonus social, one bonus research, and one bonus military, you will pay nothing for all three.

Nothing groundbreaking, but I thought it an interesting point.