I'm running into - what I expect are - common problems when using Manipulate or Dynamic. I was hoping someone could give me some tips

ControlActive

I have a plot that's refreshes very quickly when I don't set PlotTheme->"Detailed". I would like to have Gridlines, PlotLegends, etc enabled, but I would like the speed too. I've seen some improvement by using ControlActive, I'm doing something like

DynamicModule[{}, Column@{
    Slider[Dynamic[a],{a,0,10}]
    Dynamic[ControlActive[Plot[Sin[a*t],{t,0,5}],
        Plot[Sin[a*t],{t,0,5},PlotTheme->"Detailed",PlotLegeneds->{"Sine"}]]]
    }
]

Is there a cleaner way of doing that? Using ControlActive around PlotTheme gives an error.

Interacting/Onscreen Dynamics

I have an array of input fields and a column of popup menus that are on screen with the plot. When I scroll them off screen the plot runs faster. Is there a way to decouple the Dynamics of the onscreen input fields while the plot is being manipulated?