What does the gold in your treasury represent?
As we've researched currency, it does still depend on whether we would be using the civic or anything above it I'd envision. The currency itself can be established as anything at this point. Often, early currencies were simply some of the most in-demand resources around, like salt, and to some extent often still is where gold reserve still backs printed money (though that is a system beyond mere 'currency' itself really...)
But provided that's the case for these questions, I'd say that the 'gold' in the treasury represents a volume of the currency in circulation held by the central state. I understand that the volume of overall currency in the economy is subjective and may cause the value of our currency to vary (inflation) but I still see the held 'coin' as being what the state owns as opposed to what's held by private citizens. Thus the value of the actual currency itself is fairly subjective and the treasury is always a representation of its relative value rather than any kind of direct count.
When you research at 100%, you're spending your taxation income on your research efforts. Pay going back into your society via research grants/subsidies, hiring thinktank teams and in general facilitating the thinkers in your society, that does not always pan out into something profitable for society as a whole, thus you cannot count on that money going back into the coffers via taxation down the road, and at least for now, that taxation has been applied and is now used up by the state.
However, I'd think under a good strong economic setup, we'd see increasing overall economy values (deflation) from use of the other sliders such as research, culture, and espionage. Use of these should create an improved economic 'health' in your community (which we don't bother to measure right now in any way outside of using inflation/deflation to create better GAME balance) which could indeed create increased tax revenue over time.
So collecting 100% gold from your taxation and sitting on it, just allowing it to build up in your treasury, should create a rather quick decline in the overall health of the economy and lead to long term reductions in tax revenues. But if you're sliders are not 'taxing' per se, then any gold in the treasury isn't exactly harming the economy, its a result of a powerful and expansive economy that was so capable and productive that nobody really notices this portion of its overall efforts is being sat on by the state.
In fact, under this view, spending gold to 'hurry', or allocating taxation to purchasing all available labor sources in a city for a given project, should actually improve the economy overall, leading to DEflation rather than INflation. Again, the state is pouring money into its own economy here and thus employment and job values go up thus the state gains back much of it in taxes... this is basically 'the New Deal' effect.
Now, when we adopted a Central Reserve Banking system we adopted the capacity to be in-debt to a private lender. In fact, we pay interest on all money borrowed, and we start with a base of zero so we're betting on our economic growth to pay for this interest because all money IN the system HAS been borrowed! Its kinda nuts really but it works well to provide us with an ability to 'super-invest' without going into international debt (not to say that isn't another source of lending and borrowing also taking place - which sadly, civ doesn't have any function for. Between civs, gold is always gift or demand or tithe.) I see this as being poorly represented in Civ since it really represents the ability for a nation to go into the negative on gold, which we in the US are greatly in the negative to the point that pretty much all national income tax is doing nothing more than paying the interest rate on our economic debt to the Federal Reserve. The rest of what our government spends is stemming from sales, corporate and property taxation (and a number of other sources of revenue...)
We also allow our own people to purchase bonds which is another way of gradually borrowing against the economy itself, allowing the people as a whole to potentially benefit from positive economic growth. While they are hedged against loss since the interest rate is fixed, our state could end up profiting or losing out on these bonds depending on how the economy goes from the point of purchase.
(which I could do) I only put in 
.) would be quite logical as it would indicate some added mortality rate.
A good a compromise as any, and less work.
bonuses depending of Taxation tech will be ok.
